Difference between revisions of "Book - Buchanan's Manual of Anatomy including Embryology 12"

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=Chapter XII The Thorax=
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==Thoracic Wall==
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Muscles—Intercostal Muscles. — The classic description of t muscles gives them as two in number in each space, external internal, arranged as thin sheets of obliquely-disposed muscular hi with a large admixture of tendinous fibres.
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External Intercostal Muscles— Origin .—The lower border of upper rib bounding an intercostal space.
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Insertion . — The outer margin of the upper border of the lower
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Nerve-supply . — The intercostal nerve of the corresponding spat
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Fig. 577. — Diagram of the Intercostal Muscles and Intercostal Artery. A small portion of the external intercostal muscle has been divided and reflected.
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The fibres of each muscle are directed downwards and forwc and in this respect coincide with those of the obliquus exte abdominis. The muscles, as a rule, extend as far forwards as junction of the ribs with their cartilages, but sometimes they short of this point, especially in the upper spaces. From the p where the fibres cease the upper six muscles are continued inw to the side of the sternum by a thin delicate membrane, called anterior intercostal membrane. This occupies the spaces between true costal cartilages. Posteriorly the muscles extend as far as tubercles of the ribs.
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[nternal Intercostal Muscles. —
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Origin. — The upper margin of the al groove of the upper rib.
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Insertion. — The inner margin of the upper border of the lower rib. Serve-supply. —The intercostal nerve of the corresponding space, rhe fibres of each muscle are directed downwards and backwards, and lis respect coincide with those of the obliquus internus abdominis, upper six muscles extend as far inwards as the side of the sternum, the lower two are continuous anteriorly with the obliquus internus )minis. Posteriorly the muscles extend as far back as the angles le ribs. In this situation each is replaced by a delicate membrane id the posterior intercostal membrane , which lines the adjacent ion of the external intercostal muscle, and ds behind with the superior costo-transverse nent. The internal intercostal muscles are ired internally by the parietal pleura.
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4 ction of the Intercostal Muscles. — This subhas given rise to much discussion and irence of opinion. Three views are entered: (i) According to Haller, the external internal intercostal muscles both act as ators of the ribs, and are therefore muscles ispiration. Inasmuch as the fibres of the muscles decussate, they must, according to view, act on the principle of the parallelon of forces. The common nerve-supply of
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Fig. 578. — Diagram of two muscles tends to favour this view. Section across an According to Hamberger, the external inter- ntercostal pace.
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al muscles are elevators of the ribs, and El, I, external and in 'efore muscles of inspiration; whilst the inLal intercostal muscles are depressors of
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ribs, and therefore muscles of expiration.
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According to Hutchinson, the external inter:al muscles and the interchondral portions of internal intercostal muscles act as elevators the ribs, and are therefore muscles of ination; whilst the interosseous portions of the internal intercostal scles act as depressors of the ribs, and are therefore muscles of iration.
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When a rib is elevated, its lower border is at the same time
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rted.
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ternal intercostal muscles ; INT, intercost, intimus, or intracostal. Pleura represented by interrupted line. Lateral cutaneous nerve shown between El and I.
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Subcostal Muscles. — Deep to the internal intercostal muscles the lains of a third sheet of muscular fibres can often be demonstrated, i sheet is best developed dorsally and in connection with the lower ces. The direction of the fibres is similar to that taken by the cs of the internal intercostal, but unlike these last the fibres, tead of passing between adjacent ribs, pass between ribs some ces apart. The fibres constitute the subcostal muscles, which are the same plane as the sterno-costalis and the costal fibres of the diaphragm, and represent in the thoracic wall the transversus mus of the abdominal wall.
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For the levatores costarum muscles, see Index.
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It is customary, in modern descriptions of the intercostal muscu ture, to speak of three layers of muscles in this situation. 1 additional fibres are referred to as intercostales intimi: they w described and figured many years ago by Henle, and are usually tal to be partly detached fibres of the internal intercostals. Their fib have the same direction as those of the internal intercostals, from wh they are separated by the intercostal vessels and nerves (Fig. 57 They form a very thin layer, aponeurotic in some places, and tra lucent, better developed in the lower part of the thoracic wall, a more particularly in the middle portions of the spaces.
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They are frequently considered to be parts of the same sh as the sterno-costalis (triangularis sterni) and subcostal fibi but this does not seem to be at all certain. If this view is tak the three kinds of muscle are grouped together as the transver thoracis, implying their general continuity with the sheet of abdominal transversus.
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Intercostal Nerves.—These are eleven in number on each side, a are the anterior primary divisions of the upper eleven thoracic spi nerves. The anterior primary division of the twelfth thoracic spi nerve is not an intercostal nerve, but lies along the lower border the twelfth rib, and is known as the subcostal nerve (‘ last doi nerve ’).
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The lower five intercostal nerves ultimately leave the intercom spaces, and pass into the anterior abdominal wall.
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Upper Six Intercostal Nerves .—Each of these nerves, as it ent the back part of an intercostal space, lies between the posterior ini costal membrane and the parietal pleura. About the level of the an of the rib it pierces the posterior intercostal membrane, and pas forwards in the costal groove of the upper rib, lying between intercostal muscles. It continues its forward course in this posit in company with the intercostal artery and intercostal vein, the or of these from above downwards being intercostal vein, intercom artery, and intercostal nerve. The nerve is concealed by the ov lapping lower border of the upper rib.
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At (or just beyond) the angles of the ribs between which it is pass the intercostal nerve gives off a collateral branch and, a little furt on, its lateral cutaneous branch. The collateral branch runs forw; along the upper surface of the rib below the space, supplying muscles and terminating either in them or by forming a connect loop with the main nerve some distance from the sternum. The late cutaneous branch pierces the internal intercostal muscle to run forw: between this and the external muscle: it pierces this to reach the surfa the actual site of the perforation varying, of course, according to level of the nerve. The main intercostal nerves themselves run between the intercostales interni and intimi after they have given off branches described.
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laving arrived at the anterior extremity of the osseous rib, each r e, still internal to the internal intercostal muscle, passes inwards ts deep surface, lying at first upon the parietal pleura, and sublently upon the sterno-costalis muscle, crossing in its course the rnal mammary vessels. On reaching the side of the sternum it es straight forwards, to become an anterior cutaneous nerve, cing in succession the following structures: the interchondral ion of the internal intercostal muscle; the anterior intercostal ibrane; the pectoralis major muscle; and the deep fascia.
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Branches.—These are muscular, lateral cutaneous, and anterior ineous.
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The muscular branches supply the following muscles: the levatores arum, serratus posterior superior, subcostal muscles, intercostal internal mammary artery; AOR, aorta; RA, anterior primary ramus of thoracic spinal nerve; COLL, collateral branch; LC, lateral cutaneous branch; P, anterior terminal perforating, passing in front of internal mammary.
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scles, the sterno-costalis, the serratus posterior inferior, and the scles of the anterior abdominal wall.
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The lateral cutaneous nerves arise just beyond the costal angles, 1 run as described above. They pierce the external intercostal scles, and make their appearance under fibrous arches connecting costal slips of origin of the serratus anterior. The first intercostal
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ve, as a rule, gives off no lateral cutaneous branch, and that of the ond is known as the intercosto-brachial nerve.
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The anterior cutaneous nerves are the terminal branches of the upper intercostals, that of the first being sometimes absent. For their
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criptions, see Index.
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Intercostal Arteries. — These vessels are arranged in two sets derior and anterior.
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Posterior Series. — The intercostal arteries of the first two spaces ! derived from the superior intercostal artery (see Index). The intercostal arteries of the lower nine spaces are branches of the < scending thoracic aorta, and are called the posterior intercostal arten Each at first lies between the posterior intercostal membrane and 1 parietal pleura. About the level of the angle of the rib it pierces i posterior intercostal membrane, and gives off its collateral intercos branch, which inclines downwards. These two arteries now p; forwards between the two intercostal muscles, the main poster intercostal lying in the costal groove of the upper rib, where it 1 the intercostal vein above it and the intercostal nerve below it, a the collateral intercostal lying along the upper border of the lov rib. These two vessels, in the case of the upper nine spaces, termin; by anastomosing with the anterior intercostal arteries, which are t in number in each of these spaces, and will be presently describi These anastomoses take place a little in front of the mid-point betwe the vertebral column and the side of the sternum.
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Branches.—These are posterior, collateral intercostal, and late cutaneous.
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The posterior branch passes backwards to the muscles and inte^ ment of the back, giving off in its course a spinal branch, which ent< the vertebral canal through the intervertebral foramen.
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The collateral intercostal branch, as stated, arises about the le^ of the angle of the rib, and inclines downwards to the upper border the lower rib, along which it passes between the intercostal muscles.
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The lateral cutaneous branch accompanies the corresponding latei cutaneous nerve.
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The posterior intercostal and collateral intercostal arteries gi branches to the intercostal muscles and ribs. Those of the thii fourth, and fifth spaces, at least, furnish branches to the mamma gland and pectoral muscles, anastomosing with the thoracic brand of the acromio-thoracic artery from the first part of the axillary, a with the lateral thoracic from the second part of that vessel. T first posterior intercostal artery, as it enters the third intercostal spa< gives off a branch which ascends to the back part of the second int< costal space, and anastomoses with the branch of the superior intercos artery to that space.
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Anterior Series. — The internal mammary artery furnishes t' anterior intercostal arteries to each of the upper six intercostal spac and the musculo-phrenic branch of the internal mammary furnisl two anterior intercostal arteries to each of the seventh, eighth, a ninth intercostal spaces. The arteries of the upper six spaces lie first upon the sterno-costalis muscle, and then upon the parietal pleu being under cover of the internal intercostal muscle. Afterwards the anterior intercostal arteries pass between the external and inter] intercostal muscles. In each space they anastomose with the poster intercostal and collateral intercostal arteries, and also with the c responding intercostal arteries of the upper two spaces.
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Branches.—These are distributed to the intercostal muscles, ri mammary gland, and pectoral muscles.
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The lower two intercostal spaces are not furnished with anterior srcostal arteries. The posterior intercostal arteries of these spaces, sr leaving them, enter the abdominal wall, and pass forwards ween the internal oblique and transversalis muscles to the rectus lominis, in which they anastomose with the superior epigastric 1 inferior epigastric arteries.
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Intercostal Veins.—These veins accompany the corresponding
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enes.
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The posterior intercostal vein passes backwards in the costal iove of the upper rib in company with the posterior intercostal ery, above which it lies. In the region of the angle of the rib it is ned by the collateral intercostal vein , which accompanies the corremding artery. Close to the vertebral column the posterior intercostal n receives a large posterior branch, which returns blood from the iscles and skin of the back, the vertebral venous plexus, and the -tebral canal. The mode of termination of the posterior intercostal ns differs on the two sides, and will be described in connection
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h the dissection of the posterior wall of the thorax.
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The anterior intercostal veins accompany the anterior intercostal cries. Those of the upper six intercostal spaces pass to the internal immary, and those of the succeeding three spaces pass to the musculo
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renic veins.
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Intercostal Lymphatics.—The lymphatic vessels of the intercostal ices pass partly to the posterior intercostal glands, which lie at the ck parts of the intercostal ices, and partly to the anter intercostal or sternal glands, rich lie along the course of 3 internal mammary artery.
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Internal Mammary Artery.— ris vessel arises from the lower .e of the first part of the bclavian artery, and passes wnwards, forwards, and inirds behind the inner part of 3 clavicle and the first costal F IG - 580. To show the Interrelations
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of the Right Internal Mammary Artery and Phrenic Nerve, and their Relations to Subclavian and Innominate Veins (Interrupted Lines) and to Pleura.
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AP, anterior margin of pleura (PL). The mediastinal surface is stippled.
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rtilage. It then descends verbally behind the succeeding stal cartilages as low as the
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th intercostal space, where it
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minates by dividing into two
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anches—namely, the superior igastric and the musculorenic. The artery lies about ■§ inch from the margin of the sternum.
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Cervical Relations— Anterior. —The clavicular portion of the sternoistoid muscle, and the internal jugular and subclavian veins. The aenic nerve crosses it superficially from without inwards. Posterior. The dome of the pleura.
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Thoracic Relations — Anterior. —The pectoralis major; upper costal cartilages; anterior intercostal membrane; internal intercos muscles; and upper six intercostal nerves. Posterior. —The plei above, and subsequently the sterno-costalis muscle. Lateral .—1 artery has a vena comes on either side of it. The anterior intercos or sternal glands lie along the course of the vessel.
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Branches. —The artery gives off no branches in the neck. In i thoracic part of its course it furnishes the following branches:
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Pericardiaco-phrenic.
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Mediastinal.
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Pericardial.
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Sternal.
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Anterior intercostal. Perforating. Musculo-phrenic. Superior epigastric.
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The pericardiaco-phrenic artery , long and slender, arises high up, a accompanies the phrenic nerve to the diaphragm. It gives twigs the pericardium and pleura, and in the diaphragm it anastomoses w the phrenic branch of the abdominal aorta and with the muscr phrenic branch of the internal mammary. The mediastinal branc are distributed to the contents of the mediastinum—namely, remains of the thymus body, mediastinal glands, and areolar tiss The pericardial branches supply the front part of the pericardium. 1 sternal branches are distributed to the sternum and the sterno-cost; muscle. The anterior intercostal arteries . are two in number to each the upper six intercostal spaces. For their description, see Ind The perforating branches are six in number, one arising opposite e£ of the upper six intercostal spaces. Each vessel pierces the inter intercostal muscle, anterior intercostal membrane, and pectoralis maj It then gives a few twigs to the front of the sternum, and turns o wards to supply the skin of the pectoral region. The second, thi fourth, and fifth perforating branches give offsets to the inner port; of the mammary gland.
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The musculo-phrenic artery is one of the terminal branches of 1 internal mammary. It arises from that vessel in the sixth intercos space, and passes obliquely downwards and outwards behind 1 seventh, eighth, and ninth costal cartilages. About the level of 1 tenth rib it perforates the diaphragm, and terminates in the late wall of the abdomen, where it anastomoses with the ascending brar of the deep circumflex iliac artery. It gives off anterior intercos and muscular branches. The anterior intercostal arteries are two number to each of the seventh, eighth, and ninth intercostal spac in which they are disposed in a manner similar to the anterior intercos branches of the internal mammary. The muscular branches c distributed to the diaphragm and lateral wall of the abdomen, the diaphragm they anastomose with the phrenic branch of t abdominal aorta and the pericardiaco-phrenic branch of the interi mammary.
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The superior epigastric artery is the other terminal branch of i internal mammary, of which it is the continuation. It descer
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nd the seventh costal cartilage, and passes through the areolar val between the sternal and costal portions of the diaphragm. In manner it enters the sheath of the rectus abdominis, lying at first nd the muscle, but afterwards entering it. In the muscle it tomoses with the inferior epigastric artery, which is a branch of external iliac.
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'he branches of the superior epigastric artery will be found deed on p. 731.
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'he internal mammary veins (venee comites) are two in number, lie one on each side of the artery. They are formed respectively
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Sterno-hyoid Muscle Sterno-thyroid Muscle.
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Fig. 581. —Dissection of the Anterior Wall of the Thorax (Posterior View).
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The union of the venae comites of the musculo-phrenic and superior astric arteries. In their course they receive tributaries correspondto the branches of the artery. About the level of the first rcostal space the outer vein crosses over the artery and joins the r vein to form a single vessel, which opens into the corresponding 'inmate vein. The internal mammary veins are provided with ns at intervals.
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►ternal or Internal Mammary Lymphatic Glands. —These glands } a chain along the internal mammary vessels. They are usually ined, however, to the first three spaces, there being one, or it may be two, in each of these spaces. They usually lie in front of the inter mammary vessels.
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They receive their afferent vessels from (i) the inner third of mammary gland, (2) the anterior half of the costal pleura, (3) anterior halves of the external and internal intercostal muse (4) the lymphatics which accompany the superior epigastric arte and (5) the anterior group of superior diaphragmatic glands. T 1 efferent vessels pass to the thoracic duct , or to the right lymphatic d\ according to the side on which the glands lio. Frequently one more of these vessels drain to the supraclavicular group of gland? fact which explains the infection (which sometimes occurs) of th glands in malignant disease of certain abdominal viscera.
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Sterno-costalis (Triangularis Sterni) — Origin. —(1) The deep surf; of the xiphoid process and body of the sternum close to the late border, and extending as high as the level of the third costal cartila and (2) the deep surfaces of the lower two or three true costal cartila at their sternal ends.
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Insertion. — The deep surfaces and lower borders of the co? cartilages from the sixth to the second. The insertion takes pi by separate slips, and one or two of the upper slips may be partk attached to the rib itself.
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Nerve-supply. — The intercostal nerves of the adjacent spaces.
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The lowest fibres of the muscle are horizontal; the succeeding fit pass obliquely upwards and outwards; and the upper fibres are aim vertical.
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Action. — To depress the anterior extremities of the ribs, and take part in expiration. It fixes the anterior part of the chest w and so assists the actions of the muscles, particularly those of pectoral group, attached to that region.
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The muscle forms a thin musculo-tendinous sheet, which is situa on the deep surfaces of the costal cartilages and side of the sterni and is serially continuous with the transversalis abdominis mus< It supports the internal mammary vessels, sternal glands, and cert of the intercostal nerves, whilst its deep surface rests upon the park pleura.
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==Thoracic Cavity==
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Contents and their General Position. — The thoracic cavity is chk occupied by the lungs and heart. The lungs are situated one in e; half of the cavity, and each lung is provided with a serous membra called the pleura. The heart lies obliquely between the lungs, project more to the left of the sternum than to the right, and is enclosed wit a fibro-serous sac, called the pericardium. Each lung is free to exp; except at the hilum, which is situated on its inner surface. Throi this hilum the bronchus, pulmonary artery, and pulmonary v( pass, along with other structures, and the pedicle so formed is ca the root of the lung. The upper part, or apex, of the lung rises i the root of the neck, where it is covered by the cupola of the plei
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in turn being covered by the suprapleural membrane. The lower , or base, of the lung rests upon the corresponding half of the hragm, the heart lying upon the central tendon of that muscle, rhe two pleural sacs fill the spaces enclosed by the ribs of their sides, but an interval exists between them; this is the mediastinum s. 582 and 583). Nearly all the contents of the thorax (other than lungs and pleurae) lie in the iastinal space, which, as will be ., is arbitrarily divided for conience and description, rhe pulmonary artery springs a the base of the right ventricle
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he heart, and the aorta from base of the left ventricle. The innominate vein courses along upper aspect of the arch of the
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a in front of the origins of the
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)minate, left common carotid, left subclavian arteries, and
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es with the right innominate
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1 behind the sternal end of the
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right costal cartilage to form
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superior vena cava. This latter sel opens into the posteroerior angle of the right atrium he heart, and, just before piercthe pericardium, receives the a azygos which arches forwards r the right bronchus. The inor vena cava, having entered thorax through the foramen for a cava in the central tendon the diaphragm, almost lmmetely opens into the postero:rior angle of the right atrium of heart.
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The phrenic nerve on each side cends in front of the root of lung, and is intimately related the pericardium, especially on left side. The small anterior monary plexus of nerves lies in
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it of the root of each lung. The vagus nerve on each side descends ind the root of the lung, and forms in that part of its course the ch larger posterior pulmonary plexus. The following important ves descend in front of the arch of the aorta: the left phrenic, the vagus, the superior cervical cardiac branch of the left sympathetic, !■ the lower cervical cardiac branch of the left vagus. The left
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LEADING TO A COSTOPHRENIC SUL cus of Pleura (Dotted Line).
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TH is placed in the mediastinum between the pleural sacs.
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superior intercostal vein lies in front of the back part of the a arch, usually intervening between the phrenic in front and the v behind. The superficial cardiac plexus of nerves lies within concavity of the arch of the aorta, and the deep cardiac plexus behind the arch and in front of the trachea close to its bifurcc into the two bronchi. The left recurrent laryngeal nerve p; backwards under the arch, and then ascends behind it. Within concavity of the aortic arch the trunk of the pulmonary artery bn up into its right and left divisions, and the ligamentum arterioi extends from the root of the left pulmonary artery to the back ] of the concavity of the aortic arch immediately beyond the origii the left subclavian artery; the recurrent laryngeal nerve winds ro its left side prior to passing upwards behind the arch of the ao The gangliated trunk of the sympathetic lies very deeply, and desce
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Fig. 583 — Diagrams showing, in the First Figure, how the Mediasti IS SIMPLY THE INTERVAL BETWEEN THE TWO PLEURAL SACS, A DEFINI WHICH HOLDS EVEN WHEN, AS IN THE SECOND FIGURE, IT IS MUCH TENDED BY PERICARDIUM, ETC.
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The lower figure shows how the space between the pleural sacs can be div into a superior (S) mediastinum and an ‘ inferior ’; this term, howeve not commonly used, the lower space being subdivided, by the subver planes of the front and back walls of the pericardium, into a posterior (J middle (M), and a rather doubtful anterior space.
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the heads of the ribs close behind the parietal pleura, and the or three splanchnic nerves lie obliquely on the sides of the bodies ie lower thoracic vertebrae.
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The oesophagus lies in contact with the front of the vertebral mi, and the trachea is anterior to it. The descending thoracic a lies very deeply, being situated at first on the left side of the T>ral column, but subsequently in front of it. The thoracic duct ads on its right side, and the vena azygos ascends on the right of the thoracic duct, both structures being under cover of the )hagus. The superior and inferior venae hemiazygos, upper and
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r, as well as the two transverse azygos veins, upper and lower, fiosely related to the vertebral column.
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'he thoracic cavity contains the following sets of lymphatic glands : anterior mediastinal or anterior group of superior diaphragmatic ds in front of the pericardium; the superior mediastinal above pericardium, along the arch of the aorta and innominate veins; posterior mediastinal behind the pericardium; the posterior rcostal in the back parts of the intercostal spaces; and the bronchial tie interval between the diverging bronchi, and also at the root ach lung. In early life a portion of the thymus body, which is l of large size, lies behind the upper part of the sternum, whence fiends into the lower part of the neck.
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fleurse. —The pleurae are the two serous sacs which invest the
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s, and line the adjacent parietes. Each forms a closed sac, which uite distinct from its fellow. Like other serous membranes, the ra consists of two portions—parietal and visceral—which, however, continuous with one another.
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rhe parietal pleura lines the parietes, and is divisible into five ions—namely, costal, diaphragmatic, pericardial, cervical, and iastinal. The costal pleur alines the inner surfaces of the ribs and rnal intercostal muscles. The diaphragmatic pleura covers the er surface of one half of the diaphragm. The pericardial pleura 1 intimate contact with the pericardium, the phrenic nerve and •mpanying vessels alone intervening. The cervical pleura forms t is known as the cupola (dome ), and rises into the neck for about ch above the clavicle, being a little higher on the right side than file left, on account of the projection formed by the liver. The iastinal pleura of each side bounds the mediastinum. rhe viscera pleural closely invests the lung, and is known as the nonary pleura. It is intimately connected with the lung substance, extends into the fissure, or fissures, which map out the lung into s. Below the root of each lung it forms a fold, called the pulmonary went, which descends to the diaphragm; medianly the fold is icted in front on to the pericardium, and behind on to the cesogus..
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Continuity and Reflections of the Pleura —(1) In the Transverse action .—Commencing at the deep surface of the sternum, the etal pleura of each side passes backwards to the pericardium, the two being in contact except for a little inferiorly. They form lateral boundaries of the space which is called the anterior mediastin When they reach the pericardium the two pleurae separate, each keep to its own side of that sac, and so forming the pericardial plei which bounds laterally the space known as the middle mediastin Each pleura in this manner reaches the anterior aspect of the i of the corresponding lung, where it becomes the visceral pleura. 1 covers the front of the root of the lung, and then invests the en organ, dipping into its fissure or fissures, as the case may be, and gi\ a covering to the posterior aspect of the root. On leaving the b of the root of each lung, the two pleurae pass backwards slightly c the pericardium, trachea, and oesophagus, and over the descenc thoracic aorta, to the lateral aspects of the bodies of the thor; vertebrae. These portions form the lateral boundaries of the sp which is called the posterior mediastinum. From the vertebral coir each pleura passes outwards over the gangliated trunk of the sypathetic, and then lines the inner surfaces of the ribs, as well as internal intercostal muscles. In this manner it reaches the d surface of the sternum.
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Fig. 584. —Schemes to show Pleural Conditions above, through, BELOW THE ROOT OF LUNG (L). P, parietal pleura; V, visceral pleura.
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From the foregoing description it will be evident that the plei in passing from the deep surface of the sternum to the vertebral colui meets with, and is reflected over, the lung and its root. At the If of the manubrium sterni the pleura passes uninterruptedly backwa to the vertebral column. That of the right side passes over the 1 of the superior vena cava, innominate artery, right innominate v and trachea; whilst that of the left side passes over the side of left common carotid and left subclavian arteries, (esophagus, ; thoracic duct. The two pleurae, as they pass backwards at this le form the lateral boundaries of the space which is called the supe\ mediastinum.
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Below the level of the root of the lung the antero-posterior reflect of the pleura is complicated by a triangular fold, called the pulmon ligament. This fold consists of two layers of pleura in close apposition
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h are continuous superiorly with the anterior and posterior pleural
 +
stments of the root of the lung. It extends, on the one hand,
 +
veen the lower border of the root of the lung and the diaphragm i vhich latter it is attached, and, on the other hand, between the cardium and the inner surface of the lung below the level of the
 +
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. In the last-named situation its two layers separate to encase
 +
lung at that level. Its lower border is free and concave.
 +
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[2) In the Vertical Direction.—Superiorly the parietal pleura of 1 side rises in the form of a cupola into the root of the neck for about ch above the clavicle, where it is covered by suprapleural membrane sons fascia). This fascia is derived from the scalene group of teles, and is attached, on the one hand, to the medial border of the rib, and, on the other, to the front of the transverse process of the
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Fig. 585. — Diagram showing the Reflections of the Pleurae (Transverse Section).
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Hith cervical vertebra. The subclavian artery and innominate 1 are intimately related to the cupola of the pleura internally and eriorly, the artery being the higher of the two. Immediately in it of the artery the phrenic and vagus nerves and the internal umary vessels lie in contact with the pleura. Inf eriorly the ietal pleura of each side is reflected from the thoracic wall on to upper surface of the corresponding portion of the diaphragm, ch it covers where the base of the lung rests upon it. The intering portion of the diaphragm (central tendon) is covered by the )us portion of the pericardium. Medially the diaphragmatic pleura omes continuous with the mediastinal pleura.
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Lines of Reflection of the Pleurae — Sternal Reflection.- —Behind the lubrium sterni the right and left pleurae are separated from each er by an interspace which represents the superior mediastinum .
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At the level of the junction of the manubrium and body of the steri they meet each other, and descend behind the body of the bon close contact and inclining slightly to the left of the median line, the level of the lower border of the fourth costal cartilage the pleura parts company with the right, and passes outwards downwards close to the left border of the sternum, and in intin
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Fig. 586. — Surface Markings on Front of Thorax.
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Thick black lines mark pleura; dotted lines within these show lungs and ' fissures; fine lines heart and main vessels and lower edge of liver medi interrupted line shows transpyloric plane.
 +
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relation with the pericardium. There is, however, a small triang area of that sac which is uncovered by the pleura, and lies in di relation to the anterior thoracic wall. The left pleura continues downward course as far as the inner surface of the sixth costal cartil lying not far from the left border of the sternum. At this leve again passes outwards and downwards, to be reflected on to diaphragm. The right pleura pursues an undeviating course downw;
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nd the sternum as far as the junction of the body and xiphoid ess. At this level it leaves the bone, and passes obliquely outwards, iwards, and backwards over the inner surface of the seventh costal lage, from which it is reflected on to the diaphragm.
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'osto-diaphragmatic Reflection .—The level of this reflection may be idered, in the first place, as it affects certain definite vertical lines, he left sternal line it takes place at the level of the sixth costal
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Fig. 587. — Surface Markings on Back of Thorax.
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ira, thick line; lungs and fissures, dotted lines within these; uppermost level of diaphragm and liver on right side, interrupted line, hirst, sixth, and twelfth thoracic spines marked. Roots of lungs indicated.
 +
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tilage, and in the right sternal line at the level of the seventh costal tilage. In the left mammary line it takes place at the level of the ith costal cartilage, where it joins the osseous part of the rib, and the right side at a similar level. In the left mid-axillary line it es place on a level with the lower border of the tenth rib, this being lowest point to which the pleura descends. In the right midllary line it takes place on a level with the upper border of the tenth , or, it may be, the lower border. Posteriorly, in the scapular line
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(inferior angle of the scapula) on each side it takes place at the k of the lower border of the twelfth rib. From this point inwards the vertebral column the line of pleural reflection is a little below adjacent border of the twelfth rib, and is very nearly midway betw the vertebral end of that rib and the first lumbar transverse proces
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From the foregoing description it will be evident that the pie descends lowest in the mid-axillary line, and that posteriorly, d to the vertebral column, it actually descends below the level of lower border of the twelfth rib. The direction of the line of cos diaphragmatic reflection, from before backwards, is at first obliqr downwards and outwards until the level of the tenth rib is reach The line then passes backwards and upwards to the vertebral colui The costo-diaphragmatic pleural line is on a distinctly lower le than the margin of the base of the lung, but it is a little above the ] of the costal attachment of the diaphragm. The portion of diaphragm below the line is therefore in direct contact with the thoiz wall and adjacent internal intercostal muscles, without the intervent of the pleura, and the costo-diaphragmatic reflection is connected these structures by a fascial expansion.
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The free surfaces of the parietal and visceral pleurae are in hea in close contact. They are polished, and moistened by a slight amoi of serous fluid, so that they glide smoothly upon each other. In ca of pleurisy, however, certain changes take place. The free surfa become roughened by the deposit of lymph, and the movement of lung is accompanied by the sound known as pleuritic fricti Adhesions are also frequently formed, and a serous exudation tai place into the pleural sac, which tends to compress the lung injurious the condition being known as pleurisy with effusion. In cases serous exudation the cavity of the pleura, which is a shut sac, is clea demonstrable, but in health no such cavity exists, the parietal a visceral pleurae being at all times in intimate contact with each oth The attached surfaces of the parietal and visceral pleurae are rougher by fibrous processes, by means of which they are connected to 1 parts which they cover.
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The costal pleura is the thickest, and can readily be stripped fr< the inner surfaces of the ribs and internal intercostal muscles. Tb is a fairly thick layer of subserous areolar tissue on its attached surfa The diaphragmatic and pericardial pleurae are thinner than the cos pleura, and are more adherent to the subjacent structures. 1 diaphragmatic pleura follows closely the upper surface of the diaphraj in its antero-posterior curvature, with the result that though in 1 mammary line it is attached anteriorly to the eighth costal cartila it ascends when traced backwards to the level of the fifth costal cartik prior to turning downwards to the level of the twelfth rib. 1 pulmonary pleura is the thinnest and most adherent. Beneath there is a layer of subserous areolar tissue containing much elas tissue, and this is in continuity with the areolar tissue which perva( the lung.
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Differences between the Two Pleural Sacs. —The right pleural sac rises higher
 +
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he root of the neck, and is shorter and wider than the left. These differences
 +
ue partly to the projection formed by the liver on the right side, and partly 3 greater inclination of the heart to the left of the sternum than to the right.
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Ilood-supply. —The parietal pleura receives its arteries from the rior and posterior intercostals, and from the various branches of internal mammary. The visceral pleura receives its blood from bronchial arteries.
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'he veins pursue courses corresponding to the arteries, ferve-supply. —The nerves are derived from the sympathetic, nic, vagus, and intercostal nerves.
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lymphatics—Visceral or Pulmonary Pleura. —The lymphatic vessels lis part of the pleura open into the superficial lymphatics of the s. Parietal Pleura. —The lymphatics of the costal pleura open the lymphatics of the internal intercostal muscles , which terminate ) the sternal or internal mammary glands, and (2) the intercostal ds. The lymphatics of the diaphragmatic pleura open into the )hatics of the diaphragm. The lymphatics of the mediastinal pleura into (1) the anterior mediastinal glands, and (2) the posterior iastinal glands.
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'here are some costal pleural areas, however, which have particular lages. The ‘ apical ’ or cervical pleura, including that part below niddle of the first rib, drains into glands in the bottom of the neck, nd the lower end of the jugular, or it may be into the subclavian k; occasionally it seems to have some drainage into the uppermost of the axillary glands. Just below this area, and extending 1 to about the fourth rib, is a second region which, beside the lary drainage into posterior intercostal and internal mammary ds, usually has some drainage through the thoracic wall into the ary glands, accompanying the lateral intercostal nerves and vessels, drainage into axillary glands may even (but unusually) extend down r as the sixth rib.
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iructure. —The pleura is a typical serous membrane like the serous portion le pericardium, the peritoneum, and the tunica vaginalis. Such mem*s are called serous because their free surfaces are moistened by a small tity of serous fluid. Briefly stated, the pleura consists of a homogeneous, sctive-tissue basement membrane, containing elastic tissue, and lined endothelium.
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evelopment. —The pleura is developed from the walls of the coelom, or -cavity, which is the cleft in the mesoderm separating the splanchnopleure >omatopleure (see p. 78).
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'he Mediastinum. —The mediastinum is formed by the approxion of the two pleural sacs in the region of the median anteroerior line of the thorax. The interval between the two sacs is d the mediastinal space , and its boundaries are as follows: in front, sternum; behind, the bodies of the thoracic vertebra; and on either the corresponding pleural sac. The mediastinal space contains dures so numerous as to necessitate its subdivision into four parts perior, anterior, middle, and posterior.
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Fig. 588. —Mediastinal Contents exposed by pulling back the Ante
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Parts of the Pleural Sacs.
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Smaller mediastinal vessels are not shown.
 +
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and laterally, the mediastinal pleura of each side as it extends from deep surface of the manubrium sterni to the vertebral column.
 +
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Contents.—These are as follows: (1) the arch of the aorta; (2) innominate artery, and the thoracic portions of the left common car and left subclavian arteries; (3) the right and left innominate ve and the upper half, or extra-pericardial portion, of the superior \ cava; (4) the phrenic, vagus, left recurrent laryngeal, and can nerves; (5) the trachea, oesophagus, and thoracic duct; (6) the supe mediastinal glands; and (7) the remains of the thymus.
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In studying the topographical anatomy of the thorax it wT
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The superior mediastinum is situated above the pericardium, its boundaries are as follows: in front, the deep surface of the manub: sterni, with the origins of the sterno-hyoid and sterno-thyroid mus behind, the bodies of the upper four thoracic vertebrse and the I portions of the longus cervicis muscles; above, an imaginary \ corresponding to the superior aperture of the thorax; below imaginary plane passing from the lower border of the manub: sterni to the lower border of the body of *the fourth thoracic verte
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Inf. Thyroid vein L. Innominate V. Thymus
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Bulmonary A.
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d convenient to use as a landmark the manubrio-sternal joint,
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h is often sufficiently superficial to be apparent as a transverse
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3 known as the sternal angle (angle of Louis). The angle is in the 3 horizontal plane as the disc between the bodies of the fourth and thoracic vertebrae, and therefore indicates the level of the imaginary e separating the superior from the other divisions of the mediasti. The angle marks the level at which the ascending aorta ends and descending aorta begins: the superior limit of the pericardium-and
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L. Vagus N.
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L. Phrenic N.
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Sup. Intercostal Vein
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Recurrent Laryngeal N. going to turn round Lig.
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L. Appendix Infundibulum
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R. Vagus
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Cardiac Nerves
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R. Phrenic N. Sup. V. Cav.
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Ascending Aorta
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Fig. 589. — Main Mediastinal Structures seen from the Front (Heart exposed).
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The left side of the heart. At this same level the two pleural sacs meet ront, the trachea bifurcates, the vena azygos enters the superior a. cava, the left recurrent laryngeal nerve winds round the ligaitum arteriosum, the thoracic duct crosses the middle line, and the phagus reaches the middle line.
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the anterior mediastinum is situated behind the body of the num, and its boundaries are as follows: in front, the deep surface he body of the sternum, and the left sterno-costalis muscle; behind, pericardium; and laterally, the mediastinal pleura of each side as
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it extends from the deep surface of the body of the sternum to lateral aspects of the pericardium. Its direction is downwards an the left. At its upper part there is no interspace, because the pleural sacs come into contact behind the first piece of the bod] the sternum. Below this level, however, the left pleural sac dive: from its fellow, so as to leave an interspace. *
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Contents.— These are the anterior mediastinal glands, s< lymphatic vessels, the anterior mediastinal branches of the inte mammary artery, and areolar tissue.
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Fig. 590. - Transverse Section of the Thorax through the Sec Sternal Segment in Front and the Body of the Ninth Thor \ ERTEBRA BEHIND, SHOWING THE REFLECTIONS OF THE PLEURAE AND Position of the Viscera.
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S. Sternum
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A.M. Anterior Mediastinum A. A. Ascending Aorta P.A. Pulmonary Artery R.A.A. Right Appendix R.A. Right Atrium M.M. Middle Mediastinum L.A. Left Atrium
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P.M. Posterior Mediastinum O. (Esophagus
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D.A. Descending Thoracic Aorta T.V. Thoracic Vertebra M. Middle Lobe of Right Lung R.U. Right Upper Lobe R.L. Right Lower Lobe L.U. Left Upper Lobe L.L. Left Lower Lobe
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Anterior Mediastinal Glands. —These glands are situated within areolar tissue of the lower part of the anterior mediastinum, between lower part of the body of the sternum and the front of the pericardii u re f e * ve ^eir a ff went vessels from (i) the antero-median port
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ot the diaphragm, corresponding to the xiphoid process of the sternii (2) the supero-anterior surface of the liver on either side of the falcifc ligament (3) the anterior part of the pericardium; (4) the antei P 3 , 1 ^ Pr . e mec hastinal pleura. Their efferent vessels ascend and oj into the internal mammary and superior mediastinal glands.
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he middle mediastinum lies behind the anterior and below the rior mediastinum, and is the widest part of the interpleural space, ontents. —These are as follows: (1) the heart, enclosed in the ardium; (2) the ascending aorta; (3) the pulmonary trunk; ie lower half or intrapericardial portion of the superior vena cava ; he phrenic nerves and the pericardiaco-phrenic vessels; (6) the cation of the trachea; and (7) the roots of the lungs, he posterior mediastinum is situated behind the pericardium, and v the posterior part of the superior mediastinum, with which r it is continuous. Its boundaries are as follows: in front , the ardium, and below this the posterior part of the diaphragm;
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Fig. 591. — Structures in Posterior Mediastinum, seen from the Left.
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id, the bodies of the thoracic vertebrae below the level of the lower ier of the body of the fourth; and laterally, the mediastinal pleura ich side as it extends from the back of the root of the lung to side of the vertebral column.
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Contents. —These are as follows: (1) the descending thoracic aorta;
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he oesophagus, and the two vagus nerves; (3) the thoracic duct;
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he vena azygos; (5) the superior and inferior venae hemiazygos, with corresponding transverse azygos veins; (6) the greater splanchnic r es, right and left; and (7) the posterior mediastinal glands.
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Phrenic Nerve. —The nerve arises chiefly from the anterior primary sion of the fourth cervical nerve. It usually receives a small root from the anterior primary division of the third cervical, and, a rule, an additional root from that of the fifth cervical. Hat descended on the superficial surface of the scalenus anterior mu: to the root of the neck, it crosses the internal mammary artery su] ficially from without inwards. It then enters the thorax and desce in front of the root of the lung in close contact with the side of pericardium, and under cover of the mediastinal pleura. Ha\ reached the diaphragm, the nerve divides into several branches, wl pierce that muscle, to be distributed to its abdominal surface, terminal branches of each nerve are connected in the diaphragm v filaments of the corresponding phrenic plexus of the sympathe which is an offshoot from the coeliac plexus. At the place of junct
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of the two sets of fibres on right side there is a small gangli called the phrenic ganglion. the thorax the phrenic ne occupies the superior and mid mediastinal spaces. The n phrenic nerve lies in success on the outer side of the ri innominate vein and superior v< cava, and then descends in fr< of the root of the right lu Certain filaments from this ne not infrequently reach the un surface of the diaphragm passing through the vena ca aperture. The left phrenic ne: descends in the interval betw< the left common carotid £ left subclavian arteries, where crosses the vagus nerve fr without inwards. It then pas behind the left innominate vc and crosses over the arch of aorta separated from the vagus by the left superior intercostal ve after which it descends in front of the root of the left lung. E; nerve is accompanied by the pericardiaco-phrenic artery, which i branch of the internal mammary artery.
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Branches.— The nerve of each side furnishes twigs to the p< cardium, the mediastinal pleura, the inferior vena cava, peritonei liver, and suprarenal glands; its principal branches are, howet distributed to the diaphragm.
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Differences between the Two Phrenic Nerves. —(i) The right nerve is shoi, than the left, because the right half of the diaphragm, having the bulk of liver below it, is higher than the left half. (2) The right nerve is straighter til the left, because the heart, enclosed in the pericardium, projects less to the ri side than to the left. (3) The right nerve occupies a deeper position in the upl part of the thorax than the left. " }
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Fig. 592. — Structures in Posterior Mediastinum, seen from the Right.
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PH.N., phrenic nerve.
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Pericardium. — The pericardium is the fibro-serous sac which loosely ounds the heart in the middle mediastinum. It is somewhat cal, being wide below, where it is in contact with the diaphragm, narrow above, where it surrounds the great vessels connected 1 the base of the heart. On each side it is intimately related to mediastinal pleura, and is embraced by the anterior portions of inner surfaces of the lungs. The phrenic nerve on each side descends ery close contact with it. In front of it are the body of the sternum the sternal ends of the corresponding costal cartilages. Its anterior ace is to a greater or less extent encroached upon by the adjacent
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Fig. 593. — The Heart (Anterior View) and Pericardium. The anterior part of the pericardium has been removed.
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•tions of the anterior margins of the lungs and by the two pleurae, ere is, however, a small portion of this surface which is immediately ited to the sternum below the level of the lower border of the fourth
 +
 +
costal cartilage at its sternal end. Posteriorly, the pericardium
 +
in front of the posterior mediastinum, and the oesophagus is here
 +
ited to it opposite the posterior aspect of the left auricle of the heart. The pericardium consists of two portions—an external or fibrous, I an internal or serous. The fibrous pericardium is strong and dense, eriorly it is attached to the middle lobe of the central tendon of ! diaphragm, and slightly to its muscular part, more particularly on the left side. Superiorly it ensheathes the great vessels connec with the base of the heart, with the single exception of the infei vena cava.
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The fibrous layer is attached to the sternum by two fibrous ban which are known as the superior and inferior sterno-pericara ligaments of Luschka, the former being attached to the deep surf; of the manubrium, and the latter to the deep surface of the xiph process.
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The serous pericardium is a typical serous membrane, and consi of two layers, parietal and visceral, which together form a closed sa
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The parietal portion lii the inner surface of 1 fibrous part, to which it closely adherent, and a intimately covers the up] surface of the central tend of the diaphragm.
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The visceral portu known as the epicardiu closely invests the heart, a! also the great vessels at base more or less complete The continuity between t parietal and serous portic is established inferiorly alo the inferior vena ca^ Superiorly the continuity established along the gre vessels at the base of t heart about ij inches abo it. In this situation t serous portion forms an c terial sheath which enclos within it the ascending aor and pulmonary trunk 1 about ij inches, this bei the only complete shea formed by the serous portic Behind this sheath, with its contents, and in front of the atrial port! of the heart, there is a passage, called the transverse sinus of t pericardium, which leads from the right to the left side of the sero sac. The serous portion is also related to the superior vena cava ai the pulmonary veins, but it only covers them in front and at t sides.
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The serous portion of the pericardium forms a triangular fo, called the ligament of the left vena cava (vestigial fold of Marshal
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 +
which is situated between the left pulmonary artery and the upper 1< pulmonary vein. Its base is directed towards the left, and its surfac
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Fig. 594. —Scheme of Disposition of Arterial (A) and Venous Mesocardia (V) on Posterior Wall of Pericardium.
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The dotted arrow lies in transverse sinus.
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THE THORAX
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1019
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anterior and posterior. Between its two delicate layers there is nail fibrous cord, a vestige of the left duct of Cuvier; this, like the apericardial part of the superior vena cava on the right side,
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 +
es down in front of the pulmonary vessels.
 +
The free surfaces of the parietal and visceral layers of the serous don are smooth, polished, and lubricated by serous fluid to allow of movement on the part of the heart. In the course of pericarditis y become at first dry, and then roughened by deposits of lymph, s giving rise to the pericarditic friction sound, and, it may be, to esions. They may also become separated from each other by an sion into the pericardial sac.
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Blood-supply.—The fibrous portion of the pericardium and the ietal layer of the serous portion receive their arteries from (1) the icardial and pericardiaco-phrenic branches of the internal mammary, (2) the descending thoracic aorta. The visceral layer of the >us portion receives arterial twigs from the coronary arteries of the rt.
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The veins pass to the internal mammary, pericardiaco-phrenic, and gos veins.
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Nerve-supply.—The phrenic, vagus, and sympathetic nerves. Lymphatics.—These pass to the anterior, superior, and posterior liastinal glands.
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Structure. —The fibrous portion of the pericardium is composed of fibrous lie, and is very dense, but not very extensible. The serous portion consists a homogeneous, connective-tissue basement membrane containing some tic fibres, and lined with endothelium. The parietal layer is much thicker n the visceral; the latter is intimately connected with the cardiac muscular ue, except along the grooves, which are occupied by adipose tissue and 3 d vessels.
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Development. —The serous portion of the pericardium is developed from walls of the coelom, or body-cavity, which is the cleft in the mesoderm arating the splanchnopleure and somatopleure.
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The fibrous walls have various origins; the antero-lateral parts come from deep layers of the body-wall, split off by the extension of the pleural cavities, l the lower or diaphragmatic part is derived from the septum transversum.
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} cavity is at first continuous with the pleural sacs, but the openings, which dorsal and medial to the ducts of Cuvier, are closed by the end of the first nth.
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The Thymus.—This is present in the foetus and young child, a.nd ms a very conspicuous object in the dissection of a child during J first year or two of life. It attains its greatest size at puberty, er which, as a rule, it slowly atrophies, although traces of it are to found even in advanced age. The atrophic process which it under-S is, however, extremely variable. In its fully-developed condition is situated partly in the thorax and partly in the neck. In the mer situation it occupies the superior and anterior mediastinal ices, extending as low as about the level of the fourth costal cartilages, d lying in front of the great bloodvessels and upper part of the perirdium, the upper part of the sternum being in front of it. In the ck it extends as high as the lower part of the thyroid gland, being
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1020
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A MANUAL OF ANATOMY
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under cover of the sterno-hyoid and sterno-thyroid muscles. In situation it embraces the front and sides of the trachea, complel concealing it from view, and encroaches upon the carotid sheath
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either side. Its length is ab
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Two Follicles
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Trabecula
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Medulla
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Cortex
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Fig. 595. —Transverse Section of a Lobule of the Thymus Gland of a Kitten.
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The concentric corpuscles of Hassall are shown in the medulla.
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2w inches, and its breadth, wt
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is greatest inferiorly, is about inches. Its colour is pinkish is soft in consistence; and surface shows indications of lo lation. It consists of two as} metrical lateral lobes, each of wh is pyramidal. In some cases left lobe is the larger, and other cases the right. These lo are in close contact, but are s quite distinct. Sometimes a th lobe is present, occupying an termediate position between other two.
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Blood-supply.—The arteries chiefly derived from the inter mammary, inferior thyroid, s superior thyroid.
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The veins open into the rij and left innominate and thyr veins.
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Nerve-supply.—The nerves ; derived from the sympathetic a vagus.
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Structure. —Each lobe has a capsule of fibrous tissue, from which traben pass into the interior. These trabeculae map out each lobe into large and sn lobules. Each lobule consists of an outer cortical and an inner medull portion. The cortex is composed of lymphoid tissue, the lymphoid elem predominating over the retiform, and it is surrounded by a capillary r work of bloodvessels which contains many lymph corpuscles. The lymph tissue of the cortex is incompletely subdivided into nodules by means trabeculae.
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The medulla is more transparent than the cortex, the retiform element the lymphoid tissue is more conspicuous, and the lymph corpuscles are \ numerous. In addition, the medulla contains small groups of cells, more less concentrically arranged, which are known as the concentric corpuscles Hassall. According to one view, these cells are remains of the diverticula fr which the thymus body is developed; but another view is that they are conceri with the formation of bloodvessels and connective tissue.
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Development. —The thymus body is developed in two lateral parts from entodermic epithelium of the pharyngeal portion of the primitive gut. 1 epithelium of the third visceral cleft on either side becomes evaginated early the second month, and gives rise to dorsal and ventral diverticula. The vent diverticulum, which forms the thymic growth, has a thick epithelial wall, bu small lumen, and grows in a downward direction. Its distal end, which ] ventral to the pericardium, forms a solid enlargement, and the proximal d loses its connection with the third visceral cleft. The enlarged distal end grj
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THE THORAX
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1021
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umerous solid epithelial buds, which are invested with mesoderm. This ing gradually extends to the proximal part of the diverticulum. The solid and cords of each side ramify freely, and give rise to the corresponding lobe e thymus. The original diverticulum thus assumes a lobulated appearance, resembles a racemose gland. The buds or acini, however, are solid, and not w, as in racemose or acinous glands. The acini are separated by connective s and bloodvessels, which are developed from the surrounding mesoderm, phoid tissue is also developed from the mesoderm around the acini, and tissue forms the greater part of the adult thymus. The epithelial elements ch lobe are subordinate to the lymphoid tissue, and are ultimately represented le concentric corpuscles of Hassall.
 +
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jungs.—The lungs are two in number—right and left. They are lgy in consistence, float in water, and are readily compressed, m pressed between the fingers crepitation is elicited, this being to the displacement of air. When the lung is incised, similar litation is heard, and a muco-serous fluid, mixed with air, exudes, y possess considerable elasticity, their colour is that of a dark slate, they are usually mottled, this being due to carbonaceous matter, larly life, however, the colour is rose-pink.
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rhe lungs occupy the greater part of the thoracic cavity. Normally / are at all times in close contact with the thoracic walls, the pleurae rvening. Unless adhesions have formed during life between the
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eral and parietal pleurae, the surface of each lung is quite free
 +
spt in two situations—namely, at the root, which occupies a limited i of the inner surface, and at the attachment of the pulmonary ment. Each lung is conical, the base being directed downwards. >resents for consideration an apex, a base, two surfaces, and two iers.
 +
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The apex is blunt, and rises out of the thoracic cavity into the t of the neck for about inches. It is here covered by the cupola he pleura, and a little below its highest point it presents a groove its medial and anterior aspects. In the case of the right lung > groove is produced by the innominate and right subclavian arteries, l in the case of the left lung by the subclavian artery of that side, ow this groove there is another groove, produced on either side by innominate and subclavian veins.
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The base is extensive, semilunar in outline, and concave in adaptai to the upper arched surface of the diaphragm, upon which it ts, with the intervention of the pleura. The base of the right g is related to the right lobe of the liver, and that of the left lung [he left lobe of the liver, the stomach, and the spleen, the diaphragm srvening in each case. The margin of the base is thin and sharp, 1 it extends into the costo-diaphragmatic recess, reaching lowest lind, but nowhere as low as the line of the costo-diaphragmatic ection of the pleura.
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The costal surface is extensive and convex, and in health it is sely applied to the inner surfaces of the ribs and of the internal ercostal and subcostal muscles.
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The medial surface is of much more limited extent than the outer
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1022
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A MANUAL OF ANATOMY
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Fig. 596.—Mediastinal Aspect of Right Lung.
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part (DA) of the aortic groove, vertically placed and produced 1 the descending thoracic aorta. Anterior to the lower part of tf groove the left lung is related to the oesophagus, but less intimate than the right lung. The inner surface of the right lung presen above the level of the hilum grooves for the following structures: tl vena azygos (AZ), the superior vena cava (SVC) and right innomina vein, the innominate artery, the trachea (T) and oesophagus. Tl inner surface of the left lung presents above the level of the hilu grooves for the following: the arch of the aorta (A), the left subclavb
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(Figs. 596 and 597 )- The greater part of it is concave (P) in adaptat to the heart, enclosed in the pericardium, the concavity being grea in the case of the left lung on account of the projection of the he to the left side. About the junction of the anterior two-thirds c posterior third this surface presents a vertical fissure, called the hilt at which the root of the lung is situated. The medial surface of right lung, behind the hilum, is related ((E) to the oesophagus, and corresponding portion of the inner surface of the left lung prese
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CE
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p
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ivc
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A R
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THE THORAX
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1023
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jry (S), the left innominate vein, the oesophagus and thoracic
 +
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t ((E) The borders are anterior and posterior. The anterior border is 1 and short, and overlaps the pericardium, more so during inspiral than expiration, but leaving an area of the pericardium uncovered, wn as the area of precordial dulness. The anterior border of right lung keeps behind the sternum as low as the sixth right
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al cartilage. The corresponding border of the left lung, beyond
 +
lower border of the fourth left costal cartilage, presents a deep
 +
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Fig. 597. —Mediastinal Aspect of Left Lung.
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laped notch, called the cardiac notch , for the reception of the al portion of the heart enclosed in the pericardium. The posterior ier is elongated, thick, and round, and occupies the groove by side of the vertebral column.
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Each lung is divided into two lobes, upper and lower, by an exten> oblique, and deep fissure, which penetrates to the hilum. So ) is this fissure that, unless adhesions have formed, the lung appears onsist of two halves. The fissure commences on the inner surface,
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■ the posterior border, about 3 inches below the apex. It then
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1024
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A MANUAL OF ANATOMY
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turns round the posterior border, and passes obliquely downwa and forwards over the outer surface to the basal margin. In case of the right lung the fissure joins the basal margin some li distance from the lower end of the anterior border; but in the c of the left lung the fissure joins the basal margin distinctly fart forwards. A good ready guide to this fissure is the lower bordei the pectoralis major muscle, as it forms the anterior fold of the axi The upper lobe is comparatively small, and includes the ap about the upper 3 inches of the posterior border, the anterior bon and in the case of the left lung practically all that can be ausculta anteriorly. The lower lobe is of large size, and lies behind and be the oblique fissure. It includes the base, the posterior border exc
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Fig. 598.—Diagram showing the Heart and Lungs in -Situ.
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1. Tricuspid Orifice 2. Pulmonary Orifice 3. Mitral Orifice
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4. Aortic Orifice x> Region of Latham’s Circle
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the upper 3 inches, and practically all that can be ausculta posteriorly.
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By means of the oblique fissure each lung, as stated, is divided ii two lobes. In the case of the left lung the division proceeds no fartf In the case of the right lung, however, there is an additional fissr which extends from near the mid-point of the chief fissure at 1 posterior border horizontally forwards over the outer surface to anterior border. This additional fissure cuts off from the upper 1 ( a triangular or wedge-shaped portion, which is called the middle lo
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A fourth or even a fifth lobe may be present on the right side. Tb accessory lobes are usually found in the region of the hilum or of the infeij vena cava. If in the former position, the accessory lobe appears to be due t ! lateral displacement of the vena azygos, which in these cases lies in the obit fissure; if in the latter position, the accessory lobe represents the azygos lob( many animals.
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THE THORAX
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1025
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)ifferences between the Two Lungs.—(1) The right lung has two res and three lobes, whilst the left lung has only one fissure and two 3. (2) The anterior border of the right lung is uninterrupted whilst
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of the left lung presents interiorly the cardiac notch. (3) The right rger and heavier than the left, the weight of the right being about unces and that of the left about 18 ounces. (4) The right lung orter than the left, this being due to the fact that the liver causes right half of the diaphragm to rise higher than the left half, rhe right lung is broader than the left, because the heart projects e to the left side than to the right.
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Vertical Extent of the Lungs.—In the mammary line the right lung ends as low as the sixth rib; in the mid-axillary line as low as the
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Groove for Subclavian Artery. Groove for Innominate V in
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Upper Lobe .
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B
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Groove for Subclavian Artery , Groove for Innominate Vein
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Upper Lobe
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Lower Lobe Oblique Fissure
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Cardiac N otch i
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Obliaue Fissure
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Lower Lobe
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Fig. 599. —The Lungs (Anterior View), A, the right lung; B, the left lung.
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ith rib; and in the scapular line (inferior angle of the scapula) as as the tenth rib. The lower limits of the left lung exceed those he right by about the depth of a rib. It should be borne in mind, /ever, that owing to respiratory changes the vertical extent of the gs is extremely variable.
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Root of the Lung.—The root is situated at the hilum on the inner face. Its chief constituents are as follows: (1) the bronchus or tube; (2) the pulmonary artery, which conveys venous blood to lung; and (3) the two pulmonary veins, which convey the arterial oxygenated blood from the lung to the left atrium of the heart, addition to these constituents there are (a) the bronchial arteries and ns, (b) the pulmonary lymphatic vessels, (c) the pulmonary nerves, 1 (d) the bronchial lymphatic glands. All these constituents are
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65
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1026
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A MANUAL OF ANATOMY
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connected by areolar tissue, and the entire root is invested by t pleura.
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Right Bronchus
 +
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Right Pulmonary^ Artery
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Right
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Pulmonary
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Veins
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Left Pulmonary Artery
 +
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Left Bronchus
 +
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Left Pulmonary Veins
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Fig. 600.—The Roots of the Lungs (Anterior View).
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Relations. —The following relations are common to both root in front, the phrenic nerve, with the pericardiaco-phrenic artery ai
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Fig. 6oi.—Mediastinal Views of Roots of Lungs, to show Relations of Bronchi, Arteries, and Veins.
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the anterior pulmonary plex of nerves; behind, the vag nerve and the posterior pi monary plexus of nerves; ai below, the pulmonary ligament
 +
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Special Relations—Right Ro — Anterior. —The superior vei cava and the upper part of tl right atrium of the heart. S perior. —The vena azygos as arches forwards over the rig bronchus and right vagus open into the superior vena cav Posterior. — The vena azygc Left Root — Superior. —The ar of the aorta. Posterior. —T. descending thoracic aorta.
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Relative Position of the Chi
 +
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Constituents. —The relation fn
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before backwards is the same on each side, and is as follows: (i) t upper of the two pulmonary veins; (2) the pulmonary artery; ai
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THE THORAX
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1027
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the bronchus. The relation from above downwards differs on the sides. On the right side a division of the bronchus, known as eparterial bronchus, occupies the highest position at the hilum, reas on the left side a branch of the pulmonary artery is usually highest structure. The inferior angle of the somewhat pearled hilum is occupied by the lowest tributary of the pulmonary is.
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rhe larger portion of the right bronchus and the whole of the left ichus are hyp arterial.
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Itructure of the Lungs. —The trachea divides into two bronchi, right and left, structure of which is similar to that of the trachea. The right bronchus, at it | inch from its origin, gives off superiorly a branch, called the eparterial
 +
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Fig. 602. _Scheme of a Pulmonary Lobule (after I.. Testut’s
 +
 +
‘ Anatomie Humaine ’).
 +
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ichus, for the upper lobe of the right lung, and beyond this point, where it 3w hyparterial, it divides into two branches, one for the middle and the other the lower lobe. The left bronchus is entirely hyparterial, and divides into branches, one for the upper and the other for the lower lobe of the left lung, structure of these primary divisions of the bronchi is similar to that of the ichi themselves. Within each lung these primary divisions undergo subsions to a certain extent dichotomously, but the ramifications are chiefly due ranches being given off laterally, and these never anastomose. The ramificas of the air-tubes within the lungs are called the inter pulmonary hvorichi , and r ultimate subdivisions within the lobules are known as the bronchioles. h bronchiole transmits air to and from a group of infundibula.
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Each lobular bronchial tube, after entering a lobule, divides into as many nchioles as there are groups of infundibula. Each bronchiole, on approaching luster of, say, two or three infundibula, presents a dilatation, called the ibule, and from this vestibule reception chambers, known as the atria, proceed he infundibula.
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1028
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A MANUAL OF ANATOMY
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An infundibulum is an irregular, funnel-shaped passage closed at one e; and having its walls and closed extremity beset with pulmonary alveoli, wh also beset, though more sparsely, the walls of the atria.
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The interpulmonary bronchi are destitute of membranous walls posterioi and are cylindrical. This is due to the fact that their irregular plates of cartik are disposed round the circumference of the wall. The muscular fibres «  arranged in complete rings round the bronchi, and the elastic tissue for: longitudinal bundles. The mucous membrane is freely provided with racemi mucous glands, and is covered with stratified ciliated columnar epitheliu When the branches of the bronchi, by division, have attained a diameter of abc 2 1 - inch, the cartilaginous plates disappear, and the walls consist of a fibro-elas membrane and circularly-disposed muscular fibres, with a thin mucous coat des tute of mucous glands, and covered with simple ciliated columnar epithelium, th< being here and there patches of squamous, non-ciliated cells. The walls of f vestibule, atria, and alveoli are very thin, and consist of areolar, elastic, a muscular tissues, the elastic element being specially developed at the marg; of the orifices of the cells. This elastic tissue enables the alveoli to recoil at distension. The interior of the vestibule, atria, and alveoli is lined with a sin
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layer of squamous, non-ciliated epitheliu which is of extreme delicacy in the alvec Upon the outer walls of the cells there e dense networks of capillary bloodvesse which also pervade the septa between t cells, these septa being formed by infoldir of the contiguous cell-walls. Each septu contains only one capillary layer. T venous blood is thus brought into the me intimate relation with the air, all that sep< ates the two being the very thin walls the cells and the very delicate walls of t capillary bloodvessels. Moreover, there bei only one capillary layer in each intercellu] septum, the blood in the septal capillaries exposed to the air on each side.
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Bloodvessels of the Lungs. —Tv
 +
 +
sets of arteries are associated wi each lung—namely, pulmonary ai bronchial, the former having to ( with the respiratory function of the organ, and the latter with nutrition of its component tissues. The pulmonary arteries are tv in number, right and left. They result from the bifurcation of tl pulmonary trunk, and convey venous blood to the lungs. Each arte ramifies freely within the lung, its branches closely accompanying t bronchial tubes, but never anastomosing with one another. Ultimate! they terminate in dense capillary networks which lie upon the wails the alveoli, and also in the septa between adjacent cells. The arteri are somewhat more capacious than the veins.
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The pulmonary veins commence as radicles in the capillary ne works already referred to, and they pass to the root of each lun where they give rise to two pulmonary veins, which proceed to tl left atrium of the heart and convey to it arterial or oxygenated bloo The pulmonary veins and their tributaries are destitute of valve Unlike the branches of the pulmonary artery, the tributaries of tl pulmonary veins freely anastomose. Within the lung the arteri)
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Fig. 603. —Section of Lung (injected).
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THE THORAX
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1029
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ally lie above and behind the corresponding interpulmonary nchi, the veins below and in front. It is to be noted that the nonary arteries carry venous blood, whilst the pulmonary veins •y arterial blood.
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The bronchial arteries convey arterial blood to the lungs for the rition of their component tissues. They will be described in aection with the descending thoracic aorta, with which they are )ciated.
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 +
The bronchial veins return their blood chiefly into the vena azygos superior vena hemiazygos respectively. They are not so large he corresponding arteries, since some of the blood conveyed by the nchial arteries is returned by the pulmonary veins.
 +
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Lymphatics. —The lymphatic vessels of each lung are arranged wo sets— superficial and deep. At the hilum these two sets open > the interbronchial glands. The superficial set receives the lymtics of the visceral or pulmonary pleura.
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 +
Nerves. —These are derived from the anterior and posterior pullary plexuses, which are formed by the vagi nerves, aided by iches from the sympathetic. The nerves penetrate as far as alveoli, upon the walls of which they are regarded as terminating arborizations. The anterior and posterior pulmonary plexuses be found described on p. 1044.
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Development of the Respiratory Apparatus.
 +
 +
rhe respiratory apparatus consists of the larynx, trachea, and lungs. The est indication of it is a median longitudinal groove, appearing in the third c on the inner aspect of the ventral wall of the oesophageal part of the foreThis groove is called the laryngo-tracheal groove, and it produces an evaginn of the ventral wall of the oesophagus. It consists of entoderm derived 1 that of the fore-gut, and it is covered by splanchnic 'mesoderm. This groove lually deepens, and gives off the two lung-buds from its caudal end; these then carried caudally by elongation of the recess to form a trachea. The ngo-tracheal tube consists of (1) entoderm derived from that of the fore-gut, (2) mesoderm, which invests it.
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rhe condition of matters now is that there are two tubes, dorsal or pharyngophageal, and ventral or laryngo-tracheal, which communicate freely cephalad. Larynx. —The larynx is developed from the cephalic or proximal part of the nonary diverticulum, with coincident modification of the pharyngeal floor
 +
 +
the Larynx).
 +
 +
rrachea. —The trachea is developed from the caudal or distal part of the ngo-tracheal tube, the cartilaginous rings, connective tissue, and muscular ie of the trachea being developed from the mesodermic investment of the litive tube and becoming evident after the middle of the second month. Lungs. —The simple lung-buds of early stages (Fig. 604) are hollow club-shaped >dermal extensions from the caudal end of the laryngo-tracheal tube, which v into the small rounded mesodermal masses already prepared for them; e project into the upper end of the pericardio-peritoneal channels, rhe buds are asymmetrical, and grow rapidly. Various stages of this growth, 0 the middle of the second month, are given in the figure, also the outward earance of a lung a little older than this, in which the early lobulation is seen, enlarging lung, with its surrounding pleura, gains room for its growth by thing the body-wall and extending (p. 78) in this, splitting it cranially, bally, and to a smaller extent caudally. The entoderm of each lung-bud and
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A MANUAL OF ANATOMY
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1030
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of its various ramifications furnishes all the epithelial elements, bronchial ; alveolar, of the corresponding lung. The mesoderm of the bud and of its vari ramifications gives rise to the bloodvessels, connectiye and muscular tissues,; cartilages of the bronchial tubes, as well as to the visceral pleura. The pedi
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 +
of the lung-buds give rise to the bronchi. The right lung-bud gives off ti processes or vesicles, and the left lung-bud gives off two processes, and in manner the three-lobed condition of the adult right lung and the two-lo condition of the adult left lung are indicated.
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 +
Each of these processes gives rise by budding to secondary processes, : these in turn give rise successively to other processes. This budding goes very freely, and the ramifications constitute the pulmonary lobes. All the b
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 +
 +
 +
Fig. 604.— Entodermal Lung-Buds of Embryos of 5-7 and 8 mm.
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Below, at a smaller magnification, the same from embryos of fifth and si: weeks. Also outer aspect of right lung (18 mm.)
 +
 +
or processes, which carry along with them an investment of mesoderm, give 1 to the ramifying system of interpulmonary bronchi. The terminal ramificati* form the bronchioles and infundibula. The air-cells or pulmonary alveoli ;
 +
 +
formed as hollow sessile buds or evaginations of the walls of the infundibula, w the cavities of which they communicate freely.
 +
 +
As stated, the epithelial cells of the lung-buds and of all their ramificatic as well as the epithelial cells of the pulmonary diverticulum, are developed fr the entoderm of the fore-gut.
 +
 +
The eparterial bronchus is often said to be an additional bronchial outgrow The condition, however, is due in all probability to the enlargement of a si si diary arterial anastomosis; an ordinary epibronchial pulmonary artery deveL and enlarges in the second month, comparable with that on the left side, but wa
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THE THORAX
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i°3 T
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lisappears in the latter part of this month, leaving the hypobronchial artery rry on the supply to the lung.
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jungs of the Foetus. —The lungs prior to birth, having been imious to air, feel solid, like liver, and at once sink if placed in a el containing water.
 +
 +
luperior Mediastinal or Cardiac Glands. —These glands, which are Lerous and important, are situated in the superior mediastinum, g the upper aspect of the arch of the aorta, in front of the lower of the trachea, and along the right and left innominate veins, rhey receive their afferent vessels from (i) the anterior mediastinal ds, (2) the upper part of the pericardium, (3) the heart, (4) the hea, (5) the oesophagus, and (6) the thymus. Their efferent vessels
 +
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Fig. 605. —The Roots of the Lungs, etc.
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ninate in the thoracic duct and in the right lymphatic duct, or into of the main vessels opening into or forming these ducts.
 +
 +
Innominate Veins.— These vessels are two in number, right and , and each is formed by the junction of the internal jugular and clavian veins behind the inner end of the clavicle. They both in the superior mediastinum.
 +
 +
The right innominate vein is about an inch in length, and passes vnwards with a slight inclination inwards. At the level of the lower der of the first right costal cartilage, close to the sternum, it unites ft the left innominate vein to form the superior vena cava. Laterally s closely related to the right phrenic nerve and right pleura; its dial relation is the upper part of the innominate artery, and behind s the right vagus nerve.
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1032
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A MANUAL OF ANATOMY
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The left innominate vein is about 3 inches in length, and pas obliquely inwards and downwards from left to right. As stated, joins its fellow of the right side to form the superior vena cava, front of it there are the upper part of the manubrium sterni, origins of the sterno-hyoid and sterno-thyroid muscles, and the rema of the thymus. Behind it are the origins of the innominate, left comir carotid, and left subclavian arteries; the left vagus and left phre nerves; and two superficial cardiac nerves from the cervical porti( of the left vagus and left sympathetic. Below it there is the arch of 1 aorta.
 +
 +
There are no valves in the innominate veins.
 +
 +
Tributaries. —Each vein receives the following tributaries: (1) 1 vertebral vein; (2) the inferior thyroid vein; (3) the internal mamm: vein; and (4) the first posterior intercostal vein. The last-nan vessel, however, sometimes opens into the vertebral vein, and 00 sionally the right inferior thyroid vein opens into the left innomin; vein. The left innominate vein receives, as an additional tributa the left superior intercostal vein.
 +
 +
Development. —The right innominate vein is developed from that port of the right primitive jugular vein which intervenes between the place wh it receives the right subclavian vein and the place where the transverse v joins it.
 +
 +
The left innominate vein is developed from the venous network between primitive jugulars.
 +
 +
Superior Vena Cava. —This vessel is formed by the union of the rig and left innominate veins behind the lotver border of the first rig costal cartilage close to the sternum. It is about 3 inches in lengi and descends almost vertically to the level of the upper border of t third right costal cartilage, where it opens into the postero-super: angle of the right atrium of the heart. In its course it pierces t fibrous pericardium. The upper half of the vessel is extrapericardi and lies in the superior mediastinum; but the lower half is intrape cardial, and lies in the middle mediastinum.
 +
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Relations—Upper Half— Lateral. —The right phrenic nerve a: the right pleura. Medial. —The lower part of the innominate artei Lower Half— Internal. —The ascending aorta. Posterior. —The root the right lung. The serous pericardium covers the lower part the vessel except over about its posterior fourth.
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 +
The superior vena cava is destitute of valves.
 +
 +
Tributaries. —The chief tributary is the vena azygos after it h arched forwards over the right bronchus. It opens into the superi vena cava immediately before that vessel pierces the fibrous pe: cardium. Other minute tributaries are pericardial and mediastin veins.
 +
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Development. —The portion of the superior vena cava above the vena azyg is developed from that part of the right primitive jugular vein which lies beh the point where it is joined by the transverse jugular vein; and the portion bel the vena azygos is developed from the right duct of Cuvier.
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THE THORAX
 +
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1033
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nferior Vena Cava. —This vessel enters the thorax by perforatingcentral tendon of the diaphragm, and immediately afterwards
 +
 +
ceived within the fibrous pericardium. Its course in the thorax
 +
-actically nil, as it may be said to open at once into the posteroior angle of the right atrium of the heart.
 +
 +
Phoracic Aorta. —The thoracic aorta extends from the base of the ventricle of the heart to the level of the lower border of the body le twelfth thoracic vertebra. At this point it passes through the ic opening of the diaphragm, and enters upon the abdominal part
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s course. It passes at first upwards and to the right; it then
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606. —Vena Azygos and Right Sympathetic Chain, showing Ganglia and the Greater and Lesser Splanchnic Nerves arising from it.
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Ph.N., phrenic nerve.
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T s in an arched manner upwards, backwards, and to the left, over root of the left lung; and finally descends in close contact with vertebral column, lying at first upon its left side, but subsequently ■ont of it. It is therefore conveniently divided into three parts— ely, the ascending aorta, the arch of the aorta, and the descending a.
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Mcending Aorta. —The ascending aorta commences at the base lie left ventricle of the heart, behind the left border of the sternum, level with the lower margin of the third left costal cartilage, and -minates at a point behind the right border of the sternum on a level
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1034
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A MANUAL OF ANATOMY
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Fig. 607.—Transverse Section through Fourth Thoracic Vertebra (after Symington).
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THE THORAX
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io35
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A MANUAL OF ANATOMY
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1036
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with the upper margin of the second right costal cartilage. Its co is upwards and to the right, with an inclination forwards. It lk the middle mediastinum, and within the fibrous pericardium, w ensheathes it, and for about the first i| inches of its course it is enclc
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along with the adjacent portion of the pulmoi trunk, in a sheath formed by the serous par the pericardium. The ascending aorta meas about 2 inches in length. At its commencen it presents three dilatations, which corresp to the aortic sinuses in the interior, and opposite the segments of the aortic valve, sinuses are situated one' in front and behind. Along the right side of the vessel t] is a somewhat extensive dilatation, called great sinus of the aorta.
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Relations — A nterior. —The infundibulum the right ventricle, the pulmonary trunk, the right auricle at first, and subsequently first piece of the body of the sternum, f] which it is separated by the pericardium, ri pleura, and anterior margin of the right li Posterior .—The right pulmonary artery, fi Fig. 609.— Ascending which it is separated by the fibrous pericardii
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(Intrapericardial) an q the j e ft a trium, from which it is separa
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with its Three by the transverse smus. Right. — I he supe:
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Large Branches. vena cava and the right atrium. Left .—'
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pulmonary trunk.
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Branches. —These are the two coronary arteries, right and left.
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The right coronary artery arises from the anterior aortic sir Passing forwards between the right auricle and the pulmonary tru it enters the right atrio-ventricular groove, which it traverses fr front to back as far as the commencement of the inferior interv tricular groove. At this point it gives off the inferior interventricr branch. It then enters the posterior part of the left atrio-ventrici groove, in which it anastomoses with a branch of the left coron; artery. The inferior interventricular artery traverses the inferior ini ventricular groove as far as the region of the apex, where it anas moses with the anterior interventricular artery from the left coron; artery.
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The right coronary artery furnishes branches to the right atri and to both ventricles. One, of large size, called the right margi artery, passes along the right border, towards the apex.
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1 he left coronary artery arises from the left posterior aor sinus, and is at first concealed by the pulmonary trunk. It pas forward between the pulmonary trunk and the left auricle, and gn off the anterior interventricular branch. It then enters the left atr ventricular groove, which it traverses from front to back, anastomosi posteriorly with a branch of the right coronary artery. The anter
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THE THORAX
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1037
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jentricular artery traverses the anterior interventricular groove r as the region of the apex, where it anastomoses with the inferior ventricular branch of the right coronary artery, he left coronary artery furnishes branches to the left atrium and )th ventricles. One, of large size, called the left marginal artery,
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s along the left border, towards the apex.
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svelopment. —The ascending aorta, along with the pulmonary trunk, is aped from the truncus arteriosus, in which the bulbus cordis teminates. ls divided by a spiral septum into aorta and pulmonary trunk.
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rch of the Aorta. —The arch of the aorta commences behind the border of the sternum on a level with the upper margin of the id right costal cartilage, and terminates on the left side of the body
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Fig. 610.—The Arteries of the Heart seen from in Front, the Heart being supposed to be Semi-Transparent.
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Le fourth thoracic vertebra, at the lower border of which it becomes iescending aorta. It passes upwards, backwards, and to the left, ping over the root of the left lung, and when it reaches the left of the body of the fourth thoracic vertebra it descends. The ht to which the arch reaches corresponds to the centre of the ubrium sterni, which is about 1 inch below the upper border of manubrium. It lies in the superior mediastinum, and its left is in close relation with the left pleura.
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delations — Anterior .—The left phrenic and left vagus nerves, the ler being anterior to the latter. Between these two nerves are the
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rior cervical cardiac branch of the left sympathetic, and the inferior
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ical cardiac branch of the left vagus, both on their way to the super1 cardiac plexus, which they form; and the left superior intercostal
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A MANUAL OF ANATOMY
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1038
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vein on its way to join the left innominate vein. All these structu are overlaid by the left pleura. The remains of the thymus constit an additional anterior relation. Posterior. —The trachea, deep card plexus of nerves, oesophagus, thoracic duct, and left recurrent laryng nerve. Superior .— The left innominate vein, and the origins of following three great arteries, named in order from right to left, £ also from before backwards: the innominate, the left common carol and the left subclavian. Inferior .— The left bronchus, the bifurcat of the pulmonary trunk, the superficial cardiac plexus of nerves, left recurrent laryngeal nerve, and the ligamentum arteriosum. 1 last-named.fibrous cord is attached to the back part of the concav of the arch immediately beyond the level of the origin of the ] subclavian artery.
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The arch presents a constriction immediately beyond the ori of the left subclavian artery, called the aortic isthmus , and this succeeded by a short fusiform dilatation, known as the aortic spin (of His). These features are best marked in the foetus.
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Branches. —These are three in number—namely, the innomina left common carotid, and left subclavian arteries. They arise in the on named, proceeding from before backwards, and also from right to le
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Innominate Artery.— This vessel is the first and largest of the th branches which arise from the arch of the aorta. It springs from 1 upper aspect of the arch rather above the level of the upper bon of the second right costal cartilage, and it terminates behind 1 upper border of the right sterno-clavicular joint by dividing into 1 right common carotid and right subclavian arteries. It is from to 2 inches in length, its direction is upwards and outwards, and lies in the superior mediastinum.
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Relations — Anterior .— The right half of the manubrium ster with the origins of the right sterno-hyoid and sterno-thyroid muscl the left innominate and the right inferior thyroid veins; the ri£ sterno-clavicular joint; and some remains of the thymus. Posterior The trachea at first, but as the artery ascends obliquely to the ri£ it leaves the front of the trachea and is placed on the right side. 1 three cervical cardiac branches of the right sympathetic also lie behi the artery on their way to the deep cardiac plexus. Right. —The ri£ pleura; the innominate vein, with the right vagus nerve behind the superior vena cav^; and the right phrenic nerve. Left. —The 1 common carotid artery and the trachea, in this order from bet upwards.
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Branches.— These are terminal, and are two in number—name the right common carotid and the right subclavian. The artery, a rule, gives off no branches in its course. Occasionally, however, gives origin to a vessel of variable size, called the arteria thyroidea i'i (lowest thyroid artery). The interest attached to this occasioi branch is that, in ascending to the isthmus of the thyroid gland in i neck, it lies in front of the trachea, and would be endangered in 1 operation of tracheotomy.
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THE THORAX
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1039
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arieties. —(1) The innominate artery may be shorter or longer than usual, n cases of high bifurcation the artery may so encroach upon the trachea as
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endangered in tracheotomy.
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jeft Common Carotid Artery in the Thorax. —This vessel arises from ipper aspect of the arch of the aorta, just to the left of, and posterior
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Trachea
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Innominate
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Artery
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Rt. Superior Intercostal Artery
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Arch of._, Aorta
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Left Common Carotid Artery — Scalenus Anterior Muscle
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... Left Vagus Nerve
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Left Subclavian Artery (Third Part)
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Left Phrenic Nerve
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Left Superior Intercostal Artery
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Cardiac Branches of Vagus and Sup. Cervic. Symp. Ganglio 1
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Superficial Cardiac Plexus
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Left Bronchus
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Descending
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Thoracic
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Aorta
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CEsophagus
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Intercostal Vessels and Nerve
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. Abdominal Aorta
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Fig. 611.—Dissection of the Posterior Wall of the Thorax.
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the origin of the innominate artery. It lies in the superior mediasim, and its direction is upwards and to the left. Having reached posterior aspect of the left sterno-clavicular joint, it enters upon cervical part of its course.
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Relations — Anterior .—The left half of the manubrium sterni, 1 the origins of the left sterno-hyoid and sterno-thyroid muscles,
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1040
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A MANUAL OF ANATOMY
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but these structures lie at a little distance from the vessel; the L innominate vein; and some remains of the thymus. Posterior. —T trachea at first, and subsequently the left recurrent laryngeal nen the oesophagus (which here deviates slightly to the left of the trache; and the thoracic duct. Right.- —The innominate artery at first, ai later the trachea. Left. —The left vagus and left phrenic nerves, wi the superior cervical cardiac branch of the left sympathetic and t inferior cervical cardiac branch of the left vagus; the first and the 1< superior intercostal veins as they pass to the left innominate vei and the left pleura and lung.
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The thoracic portion of the left subclavian artery is on the left < and posterior to, the vessel, but at a little distance from it.
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The thoracic portion of the left common carotid artery gives < no branches.
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First Part of the Left Subclavian Artery in the Thorax. —This ves< arises from the upper aspect of the arch of the aorta a little to the 1( of, and posterior to, the origin of the left common carotid artery, lies deeply in the superior mediastinum, and is almost parallel to t thoracic portion of the left common carotid, its course being neai vertical.
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Relations— Anterior. —The left common carotid artery; the left vag and left phrenic nerves, with the superior cervical cardiac branch of t left sympathetic and the inferior cervical cardiac branch of the 1( vagus, all these nerves lying between it and the left common carol artery; and the left innominate vein. Posterior. —The oesophagus a] the thoracic duct. Right. —The trachea and the left recurrent larynge nerve. Left. —The left pleura and the inner aspect of the left lur the latter being grooved by the vessel.
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The thoracic portion of the left subclavian artery gives off branches.
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Varieties of the Aorta —1. Position.— (a) The arch of the aorta may rise high as the upper border of the manubrium sterni, or it may stop short of t level of the centre of the manubrium, (b) It may have been derived from a rh aortic arch instead of a left.
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2. Branches of the Arch and their Positions. —Varieties in these respects ; very numerous. The normal number of branches arising from the arch is thr There may be, however, only one branch, or, on the other hand, there may as many as six. When there is a reduction in the number of branches, it usually due to the left common carotid arising with the innominate from a comm trunk. The most common additional branch is the left vertebral artery, its pl< of origin being between the left common carotid and left subclavian arteri The right vertebral artery sometimes arises from the arch, but this is somewl rare. An arteria thyroidea ima may arise from the arch between the innomin; and left common carotid arteries. In rare cases the internal mammary arte or the inferior thyroid, may spring from the arch. The innominate artery n be absent, in which cases the right subclavian and right common carotid he independent origins. Under these circumstances the right subclavian art may be the last of the branches from the arch, and, when this is so, in order reach the right side of the neck, it crosses in front of the vertebral colur lying behind the oesophagus, or more rarely between the trachea and oesophagus.
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THE THORAX
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1041
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velopment of the Arch of the Aorta and its Branches. —The arch of t>rta, between the innominate artery and the left subclavian, is the ed fourth aortic arch of the embryo. It is thus of the same develop
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4
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ig. 612.—The Aorta in the Thorax, and the Principal Arteries
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of the Head and Neck.
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^rch of the Aorta Aortic Isthmus Aortic Spindle descending Aorta -oronary Arteries (from Ascend' ing Aorta) nnominate Artery ^eft Common Carotid -eft Subclavian ^ight Common Carotid
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10. Right Subclavian
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11. External Carotid
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12. Internal Carotid
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13. Maxillary
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14. Superficial Temporal
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15. Vertebral
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16. Internal Mammary
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17. Thyro-cervical Trunk
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18. Inferior Thyroid
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19. Transverse Cervical
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20. Suprascapular
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21. Superior Thyroid
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22. Lingual
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23. Facial
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24. Occipital
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25. Posterior Auricular
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26. Ascending Pharyngeal
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27. Transverse Facial
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28. Posterior Intercostals
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29. Lig. Arteriosum
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d value as the innominate and first part of the right subclavian. Beyond ft subclavian origin it is formed from a part of the left dorsal aorta. The unate, as said above, is a portion of the right fourth aortic arch, and the
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66
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1042
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A MANUAL OF ANATOMY
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left common carotid is a forward-running branch from this fourth arch, as i common carotid on the right side; these two vessels, although their actual a is in doubt, are frequently said to represent the ventral aortce of lower form interpretation of some practical value even if not absolutely correct (see p. et seq.). The left subclavian is an intersegmental artery, enlarged because < relation to the limb; its origin was from the dorsal aorta opposite to the enti of the fourth aortic arch. The ligamentum arteriosum is the remnant o: sixth aortic arch .
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For the description of the descending aorta, see p. 1089.
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Pulmonary Trunk. —This is the great vessel which, by mean its right and left divisions, carries the venous blood from the r ventricle of the heart to the lungs. It is therefore an exampl an artery which conveys venous blood, and in this respect resem the umbilical arteries of the foetus. It arises from the infundibu of the right ventricle of the heart, on a level with the upper ma of the third left costal cartilage at its junction with the stern It is directed upwards and backwards, and after a course of al 2 inches breaks up into two divisions, right and left, within the < cavity of the arch of the aorta. The vessel lies in the middle mec tinum, and along with the ascending aorta it is contained within pericardium, the serous portion of which forms one common shi for the two arteries over about the first ij inches of their course
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Relations — Anterior .—The sternal extremity of the second intercostal space and second left costal cartilage, and the left pL and left lung. Posterior .—The root of the ascending aorta; the c mencement of the left coronary artery; and the left atrium of heart. Right .—The right coronary artery; the right auricle the ascending aorta. Left .—The left coronary artery and the auricle.
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The only branches of the trunk are the two terminal divisions.
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The right pulmonary artery passes outwards to the right, be. the ascending aorta and superior vena cava, to the root of the 1 lung, where it divides into two branches, upper and lower. The u; branch is distributed to the upper lobe, and the lower branch, w is the larger of the two, is distributed to the middle and 1< lobes.
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The left pulmonary artery passes outwards to the left, in f of the left bronchus and descending aorta, to the root of the left 1 where it divides into two branches, one for the upper and the c for the lower lobe. The ligamentum arteriosum is attached to upper aspect of its root.
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The right pulmonary artery is larger and longer than the left.
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Development. —The pulmonary trunk, along with the ascending aon chiefly developed from the truncus arteriosus, but a small portion of it is foj by the commencement of the sixth left arterial arch, which remains connected that portion of the truncus which becomes partitioned off to form the pulmc trunk.
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The right and left pulmonary arteries are developed as branches fror sixth left aortic arch near its commencement, the remainder of that arch g rise to the ductus arteriosus of the foetus. I
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!
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THE THORAX
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1043
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igamentum Arteriosum.— This is a fibrous cord which is the remains important vessel peculiar to foetal life, called the ductus arteriosus. [tends from the upper aspect of the root of the left pulmonary y to the under surface of the arch of the aorta immediately nd the level of the origin of the left subclavian artery. Its tion is upwards, backwards, and slightly to the left.
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uring foetal life the right and left pulmonary arteries are of small size, and uctus arteriosus conveys the greater part of the venous blood from the ventricle of the heart into the aorta at a point beyond the origin of the left avian artery. None of this blood, therefore, can pass into the great vessels 1 spring from the upper aspect of the arch of the aorta, evelopment. —The ductus arteriosus is developed from the dorsal part of xth left aortic arch.
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'ulmonary Veins. —These vessels carry the arterial or oxygenated I from the lungs to the left atrium of the heart. Though they
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alled veins, they contain arterial blood, and in this respect rede the umbilical vein of the foetus. They are four in number,
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right and two left, and at the root of each lung the upper of the is on a more anterior plane than the lower. The right veins pass nd the superior vena cava and the right atrium, and the left > pass in front of the descending aorta. All four vessels open into eft atrium on its posterior aspect. On leaving the roots of the lungs veins are said to receive small bronchial tributaries from the cent interpulmonary bronchi and glands.
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rhe right pulmonary veins are larger and longer than those of the side.
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Tagus Nerves in the Thorax.— These nerves, right and left, differ luch from each other in their course and relations as to require rate descriptions.
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rhe right vagus nerve, having descended in front of the first part he right subclavian artery, and having given off its recurrent ngeal branch at the lower border of that vessel, enters the thoracic ty. It then descends in the superior mediastinum behind the >minate vein, and, inclining backwards, it reaches the right of the trachea, along which it courses to the posterior aspect of the of the right lung. Behind the root of the right lung the nerve )mes flattened out and breaks up into numerous branches, which disposed in a plexiform manner, and constitute the right posterior nonary plexus, from which branches are given off to the right lung, m. the lower part of this plexus the nerve issues in the form of two Is, which descend in the posterior mediastinum upon the right side he oesophagus, or gullet, and communicate freely with the corrending cords of the left side. In this manner a plexus is formed, ch is called the oesophageal plexus. Subsequently the two cords he right side unite to form a single nerve, which descends on the ‘erior surface of the oesophagus, and enters the abdomen through oesophageal opening of the diaphragm to be distributed to the -wior surface of the stomach.
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1044 A MANUAL OF ANATOMY
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The left vagus nerve enters the thoracic cavity between the common carotid and left subclavian arteries, and descends in superior mediastinum behind the left innominate vein. It passes in front of the arch of the aorta, having the left phrenic n on its right side and anterior to it, with the intervention of the supi cardiac nerve from the left superior cervical sympathetic gan^ and its own inferior cardiac branch. At the lower border of the it gives off its recurrent laryngeal branch, and then passes to
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posterior aspect of the root of the lung. Behind the root of the lung the nerve, as on the right : becomes flattened out and br up into numerous branches, w are disposed in a plexiform mar and constitute the left posterior monary plexus, from which bran are given off to the left lung. F the lower part of this plexus nerve, as on the right side, is; in the form of two cords, w] descend in the posterior mediastii upon the left side of the oesopha, or gullet, and communicate fr with the corresponding cords of right side. In this manner, as sta a plexus is formed, which is ca the oesophageal plexus. Subsequei the two cords of the left side u to form a single nerve, which scends on the anterior surface of oesophagus, and enters the abdor through the oesophageal opening the diaphragm to be distributed the anterior surface of the stomac Branches. —These are as folio the left recurrent laryngeal; card from the right nerve; pulmona pleural; oesophageal; and p cardial.
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The left recurrent laryngeal nerve arises from the left vagus in fr of the arch of the aorta on a level with its lower border. It pas backwards within the arch at the place of attachment of the li mentum arteriosum, and then turns upwards behind the arch. Hav reached the groove between the trachea and the oesophagus, it asce: therein to the neck, where its subsequent course and distribution will described. In the thorax the nerve, which contains fibres derived fr the cranial root of the accessory nerve, furnishes a few cardiac branc to the deep cardiac plexus as it winds round the arch of the aorta.
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Fig. 613. — Scheme of Vagus Nerve in Thorax and Abdomen (Flower).
 +
 +
C.P. Branches to Cardiac Plexus P.P.P. Branches to Posterior Pulmonary Plexus
 +
 +
A.P.P. Branches to Anterior Pulmonary Plexus
 +
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T.S.G. Branches from Upper Thoracic Ganglia of Sympathetic P.G. (Esophageal Plexus G.B. Gastric Branches
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THE THORAX
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1045
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ie right recurrent laryngeal nerve is extra-thoracic, inasmuch as
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es from the right vagus at the root of the neck, and it winds
 +
[ the first part of the right subclavian artery.
 +
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e left recurrent laryngeal nerve turns round the ligamentum arteriosum
 +
 +
e this structure is the remnant of the arterial arch within the sixth
 +
il arch, of which the recurrent laryngeal is the nerve. Among the visceral
 +
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in front of this the nerves are in the anterior parts of their arches, in
 +
f the arterial stems, but in the sixth visceral arch the vessel, having to >ack to reach the arch, lies in it in front of the nerve. Thus the nerve is t round the ligament when the heart and large vessels assume a more 1 position with reference to the head and neck. On the right the sixth il arch disappears early, and as the fifth artery is a very short-lived ure, the nerve catches against the fourth artery, the first part of the right tvian. It is interesting to observe that in those cases in which the right ivian arises from the left end of the arch of aorta, and passes to the right d the oesophagus, there is no right fourth aortic arch; the nerve consequently es against the third arch, internal carotid, running thus directly to the v.
 +
 +
he cardiac branches of the right vagus are two or three in number, they descend upon the trachea to the deep cardiac plexus. (The iac branches on the left side are derived, as stated, from the recurrent laryngeal nerve as it winds round the arch of the 1.)
 +
 +
he pulmonary branches are arranged in two sets, anterior and erior. The anterior pulmonary branches are two or three in her, and arise from the parent trunk before it disappears behind root of the lung. They pass to the anterior aspect of the root, being joined by sympathetic twigs, they form the anterior pulary plexus, which is reinforced by twigs from the deep cardiac us, and in the case of the left anterior pulmonary plexus by twigs 1 the superficial cardiac plexus. The branches of the anterior nonary plexus enter the lung, and accompany the ramifications he interpulmonary bronchi.
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rhe posterior pulmonary branches arise from the vagus nerve ind the root of the lung. They are larger and more numerous 1 the anterior branches, and, being joined by twigs from the >nd, third, and fourth thoracic sympathetic ganglia, they form posterior pulmonary plexus. The branches of this plexus, like those he anterior, enter the lung, and accompany the ramifications of interpulmonary bronchi. The pleural branches are distributed to mediastinal and visceral pleurae, particularly in the region of the im.
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The oesophageal branches arise chiefly from the oesophageal plexus dw the level of the roots of the lungs, and they are distributed to the tion of the oesophagus which occupies the posterior mediastinum ler oesophageal branches, however, arise above the level of the ts of the lungs, and are distributed to the portion of the oesophagus ich occupies the superior mediastinum.
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The pericardial branches arise from the oesophageal plexus, and are tributed to the pericardium, which they enter from behind.
 +
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A MANUAL OF ANATOMY
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1046
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Cardiac Plexus. —The cardiac plexus is one of three large prew bral plexuses associated with the sympathetic system, the other —namely, the cceliac and the hypogastric—being situated in abdominal cavity. The plexus is situated partly in the conca of the arch of the aorta, and partly upon the trachea above the bifu tion and behind the aortic arch. It is formed by branches of vagi and sympathetic nerves, and consists of two portions, super! and deep, which communicate with each other.
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The superficial cardiac plexus, which is comparatively smal situated in the concavity of the arch of the aorta between the ! mentum arteriosum and the right pulmonary artery. It is for by (1) the superior cardiac nerve from the left superior cervical s pathetic ganglion, and (2) the inferior cervical cardiac branch of left vagus nerve. These two nerves descend over the arch of aorta, lying between the left phrenic and left vagus nerves. At place where the two nerves join there may be a small ganglion, w is known as the cardiac ganglion (ganglion of Wrisberg).
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Branches. —The plexus gives branches to the left anterior monary plexus, and, having received a considerable accession of fi from the right half of the deep cardiac plexus, it is prolonged into right coronary plexus.
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The deep cardiac plexus, of larger size than the superficial situated upon the trachea immediately above the bifurcation behind the arch of the aorta. It is formed by (1) all the car branches of the right cervical sympathetic ganglia—namely, supe: middle and inferior—and of the right vagus—namely, superior inferior; (2) one or two cardiac branches from the right recur laryngeal nerve; (3) one or two cardiac branches from the right va in the thorax; (4) the middle and inferior cardiac branches of the cervical sympathetic trunk; (5) the superior cervical cardiac bra of the left vagus; and (6) the cardiac branches of the left recuri laryngeal nerve. It is arranged in two halves, right and left, wl communicate with each other. Each half receives the follov branches:
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Right Half.
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Left Half.
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1. The three cardiac branches of
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the right cervical sympathetic.
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2. The two cardiac branches of the
 +
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right vagus, in the neck.
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3. The cardiac branches of the right
 +
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recurrent laryngeal.
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4. The cardiac branches of the right
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vagus, in the thorax.
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1. The middle and inferior cai
 +
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branches of the left cer sympathetic.
 +
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2. The superior cardiac brand
 +
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the left vagus, in the neck.
 +
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3. The cardiac branches of the
 +
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recurrent laryngeal.
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Branches. —The right half of the deep cardiac plexus gives (1) branches to the right anterior pulmonary plexus; (2) bran< to the right coronary plexus. The left half of the deep cardiac pkj gives off (1) branches to the left anterior pulmonary plexus; (2) bran( to the left coronary plexus. j
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THE THORAX
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1047
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$.R
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Fig. 614.—Scheme of the Sympathetic Trunk in the Neck, and
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of the Cardiac Plexus (Flower).
 +
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S.C.G. Superior Cervical Ganglion.
 +
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md G.P. Branches to Vagus and Glosso-pharyngeal , 3c, 4c. Branches to Upper Four Cervical Nerves .P Carotid Plexus P. Cavernous Plexus •G. Branch to Ciliary Ganglion '.P. Deep Petrosal •P. Greater Superficial Petrosal .N. Nerve of Pterygoid Canal •N. To In f erior Ganglion of Vagus H. To Hypoglossal -.P. To External Carotid Plexus •P. To Pharyngeal Plexus •N. Superior Cardiac Nerve
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M.C.G. Middle Cervical Ganglion.
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5c. To Fifth and Sixth Cervical Nerves •P. To Inferior Thyroid Plexus •N. Middle Cardiac Nerve
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I.C.G. Inferior Cervical Ganglion.
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7c, 8c. To Seventh and Eighth Cervical Nerves V.P. To Vertebral Plexus S.P. To Subclavian Plexus I.C.N. Inferior Cardiac Nerve
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F.T.G. First Thoracic Ganglion
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Cardiac Plexus.
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C.B.Pn. Cardiac Branches of Vagus S C P Superficial Cardiac Plexus G.W. Cardiac Ganglion D C.P. Deep Cardiac Plexus R A.P.P. Right Anterior Pulmonary Plexus L.A.P.P. Left Anterior Pulmonary Plexus R.C.P. Right Coronary Plexus L.C.P. Left Coronary Plexus
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1048
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A MANUAL OF ANATOMY
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Coronary Plexuses. —These are two in number, right and left.
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The right coronary plexus is formed by branches from (1) superficial cardiac plexus, and (2) the right half of the deep card plexus. It accompanies the right coronary artery, and furnis branches to the right atrium and right ventricle of the heart.
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 +
The left coronary plexus is formed by branches which are derh chiefly from the left half of the deep cardiac plexus. It accompar the left coronary artery, and furnishes branches to the left atrium a left ventricle of the heart.
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Ganglia are met with in the coronary plexuses, and in the cou of the fibres which supply the walls of" the auricles. They are a present on the fibres which supply the walls of the ventricles the region of the atrio-ventricular groove, but nowhere else. In heart of the calf the nerves are easily recognized beneath the visce pericardium, as they pass across the muscular fibres in an obli( manner.
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Heart. —The heart is a hollow muscular organ, which, enclo: within the pericardium, is situated in the middle mediastinum, wh it lies obliquely between the two lungs. It is conical in shape, a is free to move within its pericardial sac, except at the base, wh it is connected with the great bloodvessels. Its relation to the thora wall during life is influenced by posture and by the respiratory mo merits. When a person lies upon the left side, or when the prc position is assumed, the organ is more intimately related to the thora wall than in the opposite postures; and during inspiration it is 1 intimately connected with the thoracic wall than during expiration.
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General Relations and Topography. —The heart lies obliqu behind the lower three-fourths of the body of the sternum. Ab( two-thirds of the organ are contained in the left half of the thora cavity, and about one-third in the right half. The base is direcl upwards, backwards, and to the right, and lies opposite the bod of the middle four thoracic vertebrae—namely, the fifth, sixth, seven and eighth. The apex is directed downwards, forwards, and to 1 left, and during life it strikes the thoracic wall in the fifth left int costal space if inches below the left nipple, and about £ inch witl the left mammillary line. This point represents the apex-beat, and about 3I inches from the median line of the sternum. The sten costal surface , which is convex, lies behind the lower three-fourths of 1 body of the sternum and the corresponding costal cartilages, right a namely, the third, fourth, fifth, and sixth—more particularly the of the left side. This surface is encroached upon by the pleurae a the thin anterior margins of the lungs. Opposite the cardiac not on the anterior margin of the left lung there is a small portion which uncovered by lung, unless during deep inspiration, and this cor: sponds with the area of precordial dulness. Latham’s circle is tak as defining this area, and the directions for describing the circle a as follows: Make a circle of 2 inches in diameter round a point nr way between the left nipple and the end of the sternum/ Strict
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 +
THE THORAX
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1049
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.king, the area of precordial dulness is triangular in conformity to V-shaped cardiac notch on the anterior margin of the left lung, it may be mapped out by the following lines: one drawn from the tion of the apex-beat to the median lines of the sternum on a level 1 the fourth left costal cartilage; another drawn from the position he apex-beat to the median line of the sternum at the junction he body and xiphoid process; and a third connecting the inner 5 of these two lines, and extending along the middle of the sternum.
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>rax, may be indicated with approximate accuracy in the following nner:
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 +
Base .—Draw a line across the sternum on a level with the upper rder of the third right and the lower border of the second left costal
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1050
 +
 +
 +
A MANUAL OF ANATOMY
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 +
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cartilages, and prolong this line for § inch to the right of the sterm and i inch to the left of it.
 +
 +
Inferior Border , or Acute Margin .—Draw a line from the steri end of the sixth right costal cartilage to the position of the apex-be; This line corresponds to the lower limit of the heart.
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 +
Right Limit .—Draw a line from the upper border of the third rig costal cartilage, \ inch from the sternum, to the sternal end of t
 +
 +
sixth right costal cartilage. This line shoi be curved outwards to such an extent tf its greatest convexity will be i J inches dista from the median line of the sternum, corresponds with the right limit of the rig atrium.
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Left Border, or Obtuse Margin .—Draw line from the lower border of the second 1< costal cartilage, i inch from the sternum, the position of the apex-beat. This line shor be slightly curved outwards, but it must n include the left nipple. It corresponds to t left limit of the heart.
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Course of the Circulation. —The interior the heart is divided by two septa (atrial ai ventricular) into two halves, right and le and each half is subdivided by a transvei constriction into two chambers, an upper atrium, and a lower or ventricle, right ai left respectively. The atria, except in t foetus, are completely separated from ea other by a septum, and so also are t ventricles; but the atrium and ventricle each side communicate freely with each oth by the atrio-ventricular orifice. The rig atrium receives the venous blood chiefly fro the superior and inferior venae cavae and t coronary sinus. From the right atrium t blood passes into the right ventricle, ai thence into the pulmonary trunk. The rig and left pulmonary arteries convey it to t lungs, and in passing through the pulmona capillaries it is oxygenated and beeom arterial blood. It is then taken up by the pulmonary venous radick and conveyed to the pulmonary veins, which carry it to the left atriu of the heart. From the left atrium it passes into the left ventric whence it is driven into the aorta. The aorta and its various ran fications convey the arterial blood to the different parts of the bod and thereafter it is returned as venous blood to the right atrium the heart.
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Exterior of the Heart. —The exterior of the heart presents distinj
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Fig. 616.—To show the Parts of Heart as
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SEEN FROM THE FRONT,
 +
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when Pericardium is
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REMOVED.
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VD is the right ventricle, narrowing upwards (infundibulum) to reach pulmonary artery (P). The prominent anterior part of left ventricle (VS) is seen along its left border, and forms the actual apex; the left auricle (AS) shows just above this. The ascending part of aorta (A) comes from the left ventricle, and therefore appears from behind P. AD is the anterior aspect of the right auricle.
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THE THORAX
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IQ5 1
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cations of its division internally into four chambers. These take form of grooves—namely, atrio-ventricular, interatrial, and inter tricular.
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The atrio-ventricular groove , which is deep, divides the heart into al and ventricular portions, and surrounds the organ except in it, where the root of the aorta and the pulmonary trunk are situated.
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atrial portion is posterior and superior in position, whilst the
 +
itricular portion is anterior and inferior. The right half of the io-ventricular groove contains (i) the right coronary artery, and the small cardiac vein, which latter lies chiefly in its posterior •t. The left half of the atrio-ventricular groove contains (i) the
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coronary artery; (2) the right coronary
 +
ery, which lies in its posterior part; a portion of the great cardiac vein, ich lies in its anterior part, and also jhtly in its posterior part; and (4) the unary sinus, which lies in its posterior
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rt. ! '
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The atrial portion of the heart has the m of a crescent, the horns of which present the auricles, and are directed 'wards. The concavity of the crescent also directed forwards, and lodges the ot of the aorta and the pulmonary ink, the latter being the more anterior the two. Its walls are thin, and it is vided into two atria, right and left. The ternal indication of this division is the ter atrial groove, which is situated verbify on the posterior surface to the left the openings of the superior and inferior mae cavse. This groove corresponds to Le posterior attachment of the atrial ptum in the interior. The greater part
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the posterior surface of the atrial portion .
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formed by the left atrium. Projecting forwards from the anterior id upper part of each atrium is the auricle (auricular appendix). I ho vo auricles embrace between them the root of the aorta and the
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ulmonary trunk. .
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The right atrium (right auricle) forms the anterior and right part
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f the base of the heart, and is triangular in outline as seen from ie front. The superior vena cava enters its atrium at the posteroiperior angle, and the inferior vena cava at the postero-mferior ngle. Near the latter vein the coronary sinus also opens into the trium. The right auricle (auricular appendix) is prolonged forwards rom the antero-superior angle of the atrium, and inclines to the e t 1 front of the root of the ascending aorta. It is shorter, broader, an ^ss curved than the left auricle, and its margin is notched, but no so
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Fig. 617.—A Posterior View of the Heart, showing Left Atrium (LA) receiving Pulmonary Veins (PV).
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This is the highest and most posterior cavity. The right atrium (RA) is seen beside it, "and the left ventricle (LV) is visible below and in front on its left side. The coronary sinus (SV) runs transversely between the atrium and the ventricle.
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1052
 +
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 +
A MANUAL OF ANATOMY
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much so as is that of the left auricle. The right atrium is travers< by a groove, called the sulcus terminalis , which extends from the fro: of the termination of the superior vena cava to the front and rig] side of the termination of the inferior vena cava. This groove sho\ where the sinus venosus of embryonic life meets the primitive atrium.
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The left atrium (left auricle) forms the posterior part and left the base of the heart. It is quadrilateral, and the greater part it lies flattened behind the ascending aorta and the pulmonary trun The pulmonary veins, two right and two left, open into the posteri part of the atrium. The left auricle (auricular appendix) is prolongi forwards from its left aspect, and inclines to the right over the le side of the pulmonary trunk. It is longer, narrower, and more curvi
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than the right auricle, and its margin is more deeply notched. T] back of the left atrium is related to the oesophagus, with the inte vention of the pericardium; the small oblique vein of left atrium (ve of Marshall) passes downwards and inwards upon it, to open into tl coronary sinus.
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The ventricular portion of the heart is conical, its walls are thic and it is divisible into two ventricles, right and left. The extern indication of this division is the interventricular groove, which co responds to the attachment of the ventricular septum in the interio This groove consists of two parts, anterior and posterior. The anteri interventricular groove extends over the sterno-costal surface of tl heart from the left side of the pulmonary trunk to the inferior bord
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THE THORAX
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ic>53
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he right of, and near, the apex. At this point it becomes continuous
 +
h the inferior interventricular groove. It contains, besides fat, the anterior branch of the left coronary artery, and (2) a part of great cardiac vein. The inferior interventricular groove is situated the inferior surface of the heart, and, as stated, is continuous with preceding. It contains, besides fat, (1) the inferior interven:ular branch of the right coronary artery, and (2) the middle cardiac n.
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The ventricular portion of the heart presents an apex, a base, ) surfaces, and two borders. The apex is directed downwards, wards, and to the left, and forms the apex of the heart. The left
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Great Cardiac Vein
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Left Ventricle
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Apex
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Arch of Aorta
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Superior Vena Cava
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Right Pulmonary Veins *
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'• Right Atrium
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Inferior Vena Cava
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Coronary Sinus
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Right Coronary Arteiy
 +
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Right Ventricle
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Pulmonary Trunk
 +
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Left Pulmonary Veins
 +
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Fig. 619. —The Heart (Posterior View.)
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itricle alone enters into its formation. The base is directed upwards,
 +
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kwards, and to the right, and is connected with the atria and the
 +
gins of the aorta and pulmonary trunk, the former being behind I the latter in front.
 +
 +
The surfaces are sterno-costal and diaphragmatic. The sternotal surface is convex, and is traversed by the anterior interventricular >ove. As this groove lies near the left border, the greater part of s -surface (about two-thirds) is formed by the right ventricle, and ' remainder b}^ the left ventricle. In post-mortem examinations, before, when the pericardium is opened, the right ventricle is chiefly xised for inspection. On this aspect of the right ventricle there
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the anterior cardiac veins. Its upper and left part is somewhat
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1054
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A MANUAL OF ANATOMY
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conical, and is called the infundibulum (conus arteriosus). It gr origin superiorly to the pulmonary trunk. The diaphragmatic surf is flat, and is traversed by the inferior interventricular groove, this groove lies near the inferior border, the greater part of this surf; (about two-thirds) is formed by the left ventricle, and the remaim by the right ventricle. On this aspect of the left ventricle there ; the posterior cardiac veins.
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 +
The borders are inferior (right) and left. The inferior border comparatively long, and extends from right to left. It is formed the right ventricle, and is sharp in outline, from which circumstai it is known as the acute margin. The marginal branch of the ri^ coronary artery and one of the anterior cardiac veins lie along
 +
 +
The left border is shorter th the inferior, and is blunt a round, from which circu stances it is known as 1 obtuse margin. The margi] branch of the left corom artery lies along it.
 +
 +
Interior of the Heari Right Atrium (Right Auric —The wall of the auricle marked by a number muscular elevations arran^ as closely-set, vertical, par lei bands, like the teeth a comb, from which circu stance they are called 1 musculi pectanati. Th bands, relatively to ez other, are more or less r icular. They are also presi on the right wall of 1 atrium, being more comb-1 here than in the auric and they terminate posteriorly at a vertical ridge, called the cn termmalis. This crest corresponds in position to the sulcus termini externally, and it has the same significance. Internally and posterio the walls of the atrium are destitute of musculi pectinati, and p sent a smooth appearance. The right atrium presents the follow: openings : the opening of the superior vena cava; the opening of' inferior vena cava; the opening of the coronary sinus; the openings the venae cordis minimae; and the tricuspid orifice.
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 +
The orifice of the superior vena cava, which is destitute of a val is situated at the postero-superior angle of the atrium. It is direc downwards and forwards, and the upper part of the crista termin; is continuous with its anterior margin.
 +
 +
The orifice of the inferior vena cava is situated at the poste
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Fig. 620.—Diagrammatic Section along Right Side of Heart.
 +
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AV, atrio-ventricular valve ; C, trabeculae carneae; E, valve of I VC; FO, fossa ovalis; P, papillary muscle; SV, supraventricular crest; T, opening of coronary sinus.
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THE THORAX
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1055
 +
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erior angle of the atrium, and is directed upwards and inwards,
 +
front of the orifice, and to a certain extent overlapping it, there a crescentic fold of endocardium, which is the remains of the valve the inferior vena cava (Eustachian valve) of foetal life. The conxity of the crescent is continuous with the anterior margin of the fice of the vein, and the inner horn of the crescent is continuous th the anterior limb of the annulus ovalis, to be presently described. ie fold is a somewhat indefinite structure in the adult, being subject much variety as regards size, and sometimes presenting several ■all openings. During foetal fife, however, the valve is of the utmost portance, inasmuch as it directs the blood entering by the inferior na cava through the foramen ovale into the left atrium.
 +
 +
The orifice of the coronary sinus is situated between the valve of 3 inferior vena cava and the tricuspid orifice. It is guarded by a licate semicircular fold of the endocardium, called the valve of the ■onary sinus (Thebesian valve), which, however, is functionally
 +
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ompetent.
 +
The foramina venarum minimse (foramina Thebesii) represents Tral minute openings on the wall of the atrium. Some of these are lply blind recesses, whilst others are the orifices of minute veins, led the vence cordis minimce, which return the blood from the wall the atrium.
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The atrio-ventricular or tricuspid orifice is situated in the lower i anterior part of the atrium in front of the orifice of the inferior 1a cava, with the intervention of that of the coronary sinus. It is il and in health will admit three fingers. Through this opening s blood passes from the right atrium into the right ventricle, its urn being prevented by the tricuspid valve, which will be described connection with the right ventricle.
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 +
The posterior wall of the atrium corresponds to the atrial septum,
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I presents for consideration the fossa ovalis and the annulus ovalis. The fossa ovalis is an oval depression which is situated upon the rer part of the atrial septum a little above and to the left of the free of the inferior vena cava. It indicates the position of the amen ovale of the foetal heart, which is a communication between ! two atria through which the blood entering the right atrium by • inferior vena cava passes into the left atrium. The floor of the sa ovalis is very thin, and is bounded above and at the sides by a >minent crescentic margin, called the annulus ovalis. The annulus ieficient below, and the concavity of the crescent is directed downrds. Its anterior limb is continuous with the valve of the inferior ia cava. In some cases a minute oblique communication between
 +
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two atria persists in the adult, being situated under cover of the
 +
^er portion of the annulus ovalis.
 +
 +
Interior of the Right Ventricle. —When exposed to view in the ■inary way, the interior of the right ventricle is pyramidal, the
 +
 +
e being directed backwards and to the right, and the apex forwards,
 +
the left, and a little downwards. It is completely separated from
 +
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 +
A MANUAL OF ANATOMY
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1056
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the left ventricle by the ventricular septum, which forms the poster wall of the ventricle, and bulges into it so as to be convex towards In transverse section, therefore, the right ventricle is semilunar, wall, which is about three times thinner than that of the left ventri( is thickest at the base, and becomes thinner towards the apex. 1
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\
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L. Atriiin
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“A. V. orifi
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Aortic
 +
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Vestibule
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Septum
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tiG. 621 .—-Longitudinal Section through Heart, opening the Four
 +
 +
Cavities.
 +
 +
Shows the deep situation of the aortic vestibule, between the left A.V. openi and the interventricular septum. The thin upper part of this septum the pars membranacea, which is partly between the aortic vestibule a each of the right-sided cavities. Based on a section given by Tandler.
 +
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capacity of the ventricle is about 4 ounces. Its upper and left pz form the infundibulum [conus arteriosus), from the upper part of whi the pulmonary trunk springs. The walls of the infundibulum 2 smooth, but elsewhere the walls of the ventricle are elevated in muscular bands, called trabeculce carnece . These project into t
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 +
THE THORAX
 +
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1057
 +
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y, and from their reticular arrangement they render the wall
 +
irregular. According to the manner in which the trabeculse ese are attached to the wall, they are arranged in three sets: (1) some simple elevations, which are attached to the wall by their entire th, as well as by their extremities; (2) some are attached to the only by their extremities, being free elsewhere; and (3) others ittached only by one extremity. These latter are called papillary
 +
 +
les. They are conical, and their bases are attached to the wall
 +
le ventricle. Their free extremities are connected with a number iform processes, called chordce tendinece, which pass to the margins ventricular surfaces of the segments of the atrio-ventricular e. When the ventricle contracts, the papillary muscles also ract, and by tightening the chordae tendineae they prevent the >s of the atrio-ventricular valve from being swept back into the im. The cusps are therefore maintained in contact during the
 +
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ricular systole, and no regurgitation of blood from the ventricle
 +
the atrium is allowed in health. The papillary muscles are ,nged in three groups—anterior, inferior, and septal—and their
 +
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s are attached to the walls of the ventricle in the region of the
 +
t of the cavity. The anterior papillary muscle is of large size, inferior is usually broken up into two or more secondary papillary
 +
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cles, while the septal muscles are variable both in number and
 +
In most hearts a fleshy column, called the moderator band , is met 1 in the right ventricle, which extends from the ventricular septum he base of the anterior papillary muscle. The term moderator band applied to this bundle in the mistaken belief that it moderated ension of the right ventricle. It is now known to serve for the sage of an important slip of the atrio-ventricular bundle. (The d was noted and drawn by Leonardo da Vinci more than four hunI years ago, and the name of bundle of Leonardo has been suggested it.)
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The openings. connected with the right ventricle are two in number amely, the tricuspid and pulmonary, Ihey are situated at the e of the cavity, and are guarded by most important valves. The uspid orifice is situated on the right and posteriorly, whilst the monary orifice is situated on the left and anteriorly, being also on igher level than the other. Vence minimce cordis are said to open
 +
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i the right ventricle. . .
 +
 +
The right atrio-ventricular or tricuspid orifice is oval, and admits passage of three fingers. It allows the venous blood to flow from right atrium into the right ventricle, and in order to prevent urgitation of blood from the ventricle into the atrium during the itricular systole it is guarded by an important valve, called the lit atrio-ventricular or tricuspid valve. This valve is composed of ee segments or cusps , which are covered with endocaidium. These >ject into the cavity of the ventricle, and are triangular. The bases the cusps are continuous with one another, and form a ring, which
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A MANUAL OF ANATOMY
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1058
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is attached to the margin of the tricuspid orifice. The largest cus situated in front and to the left of the tricuspid orifice. It interv< between that orifice and the infundibulum, and is known as the ante cusp. Another cusp is situated behind the tricuspid orifice, and i contact with the ventricular septum. It is called the medial c The third cusp is situated to the right near the acute margin, an called the inferior cusp. In the angular intervals between the b parts of the three large cusps there are usually three small cusps.
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Each cusp consists of two layers of endocardium, with fibi tissue between them, especially at their central parts. The mi< portion of each cusp is therefore thicker than the marginal porti these latter being thin and transparent. The margins themse
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Superior Vena Cava .
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Aorta
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Annulus Ovahs
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Fossa Ovalis
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Valve of Inferior Vena Cava
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✓ Pulmonary Trunk (opened)
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§N — Pulmonary Valves
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Orifice of Coronary Sinus
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Valve of Coronary &§§!!
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Sinus / Inferior Vena Cava
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Tricuspid Valve
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- Left Coronary Artei j
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Ventricular Septun
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Left Ventricle
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Chordas Tendineae
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I
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Papillary Muscle
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Fig. 622.—The Interior of the Right Auricle and Right Ventrici
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are notched. The atrial surfaces of the cusps are smooth, but t ventricular surfaces are roughened by the chordae tendineae, wl are also attached to the margins.
 +
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The chordae tendineae are filiform, fibrous processes which connected on the one hand with the wall of the ventricle, and the other with the cusps of the tricuspid valve. Most of them sp from the anterior and inferior papillary muscles, but a few of ti arise from the ventricular septum and from the small papillary t nences upon it. Those which are connected with the anterior papil muscle pass to the interval between the anterior and inferior cu: those which are connected with the inferior papillary muscle and subdivisions pass to the interval between the medial and infe
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THE THORAX
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1059
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>s; and those which are connected with the ventricular septum
 +
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to the interval between the anterior and medial cusps. The
 +
lection of the chordae tendineae with the cusps of the valve is of reef old nature as follows: (1) most are connected with the marginal
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s of the cusps; (2) others are connected with the thickened central
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ion of each cusp; and (3) a few pass to the basal portion of each
 +
), where they are connected with the fibrous ring around the uspid orifice.
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rhe pulmonary valve guards the orifice of the pulmonary trunk, prevents regurgitation of blood from the trunk into the right tricle during the elastic recoil of the arterial wall. It is composed
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hree semilunar cusps, and the wall of the artery opposite each
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Ascending Aorta (opened)
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Aortic Semilunar Valves —
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Ventricular Septum
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Pulmonary Trunk Lunule
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Pulmonary Veins
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Atrial Septum
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Mitral Valve
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%
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%\ t ',!■/
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- Chord® Tendineae
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r Papillary Muscle
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Trabeculae Carneae <
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Apex
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Fig. 623. —The Interior of the Left Atrium and Left Ventricle.
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ment presents a recess, these recesses being called sinuses. The ve and the sinuses are similar to corresponding structures in mection with the aortic orifice, and will be fully described along h that orifice.
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Interior of the Left Atrium.— The musculi pectinati are present V in the auricle, whereas in the right atrium they are present both be auricle and on the right wall of the atrium. The wall of the left him is entirely smooth. The atrium presents five openings— nely, the openings of the four pulmonary veins, and the mitral ice.
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The orifices of the four pulmonary veins are situated on the posterior h of either side, two right and two left, and are destitute of valves.
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io6o
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A MANUAL OF ANATOMY
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The auriculo-ventricular or mitral orifice is situated in the ante: part of the floor of the atrium. It is oval, and in health admits i passage of two fingers.
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Venee minima cordis are said to open into the left atrium.
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The atrial septum presents a slight depression, limited inferio by a faint crescentic ridge, the concavity of which is directed upwar These indicate the position of the foramen ovale of the foetal heart
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Interior of the Left Ventricle.—The cavity of the left ventri extends quite to the apex of the heart, and is longer and narrow than that of the right ventricle. It is somewhat conical, the base bei directed backwards and upwards. The ventricular septum rece<
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from the cavity, and is cones towards it. In transverse secti<
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Left
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Ventricle
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Right Ventricle
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Left Ventricle
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therefore, the left ventricle is o\ or nearly circular. The wall of 1 left ventricle is about three tin thicker than that of the right, 1 difference being readily accounl for by the fact that the left ventri is concerned with the systemic c culation, whilst the right ventri has to do with the pulmonary c culation, the latter involving a mr shorter circuit. The wall of 1 left ventricle attains its maximi thickness about the junction the upper fourth and lower thr fourths, and is thinnest in 1 region of the apex. The capac of the ventricle is about 4 ounc
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Ventricular Septum
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Fig. 624. Transverse Sections of 'ppg portion of the cavity imme
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. ateiy below the aortic orifice
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A. through apex .(superior view). known as the aortic vestibule, i
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B, through ventricles (inferior view). .. . . . . *
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walls 01 which are fibrous.
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The left ventricle, like the right, is provided with trabeculae carnt They are arranged in a very intricate manner, more particularly the region of the apex and over the posterior wall. The aor vestibule and the ventricular septum, at least over its upper pa are destitute of trabeculae carneae, and present a smooth appearan The papillary muscles are much larger than those in the right ventric they are two in number, anterior and posterior, and they are attaci by their bases to the respective walls of the ventricle, whilst th free ends are connected with the chordae tendineae.
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The openings connected with the left ventricle are two in numl —namely, mitral and aortic. They are situated at the base of 1 ventricle in close proximity to each other, and are guarded by imports valves. The mitral orifice is situated on the left and posterior whilst the aortic orifice is situated on the right and anteriorly. 1
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THE THORAX
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1061
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ic orifice is also considerably the higher of the two. Vence minima
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lis are said to open into the left ventricle.
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The auriculo-ventricular or mitral orifice is oval, and in health fits two fingers. It allows the arterial blood to flow from the left um into the left ventricle, and in order to prevent regurgitation blood from the ventricle into the atrium during the ventricular tole it is guarded by an important valve. This valve is called the auriculo-ventricular, mitral, or bicuspid valve. It is composed two large segments or cusps , with two small cusps in the angular irvals between their basal parts. The cusps are similar in shape
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L.
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'ig. 625. —Dissection (viewed from above) of the Basal Part of the
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Heart.
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3 two arterial stems have been removed close to their origins, exposing their valves, while the atria have been cut away a little distance above the atrio-ventricular valves. The coronary arteries are thus exposed for some extent after their origins, the aortic sinuses are partly visible, the coronary sinus is seen opening into the right atrium, and the atrioventricular valves, mitral and tricuspid, are seen closed.
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Pulmon. Art.
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Coron. Art.
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Coron. Sinus Left Atrium
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d structure to those of the tricuspid valve, but on account of 3 nature of their work they are thicker and stronger. They 5 disposed obliquely, and are of unequal size. The larger of 3 two is placed in front and to the right of the orifice. It internes between the mitral and aortic orifices, and is known as the terior cusp. The smaller cusp is placed behind and to the left of 3 orifice, and is known as the posterior cusp.
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The chordae tendineae are attached to the cusps, as in the case of e tricuspid valve. They are, however, fewer in number, and of safer thickness and strength than on the right side.
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1062
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A MANUAL OF ANATOMY
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Function of the Tricuspid and Mitral Valves. —These valves serve to prev regurgitation of blood from the ventricles into the atria during the ventrici systole. Whilst the ventricle is being filled, some of the blood gets beh the segments of the atrio-ventricular valve—that is to say, between each segm and the wall of the ventricle—and the segments are thus carried towards atrio-ventricular orifice. When the ventricle is filled with blood the segme are in contact, and the ventricular systole now takes place. At the same t: the papillary muscles contract. Blood is forced against the segments of the va' but it cannot in health enter the atrium, because the segments are maintai in close contact, and are prevented from being swept back into the auricle by chordae tendineae, which are under the control of the papillary muscles. If tl were no papillary muscles, in which case the chordae tendineae would spi directly from the wall of the ventricle, then the segments of the valve would be held tight, but would, under the pressure of the blood, be driven back into atrium, and regurgitation of blood would of necessity occur. The explanai of this lies in the fact that when the ventricle contracts a kind of screwing or wringing movement takes plac§ in its wall, as, so to speak, in wringing a towel. The effect of this peculiar action is to approximate successive part: the ventricular wall to the atrio-ventricular orifice, and this would have effect of relaxing the chordae tendineae, and so allowing the segments of the va to be driven back into the atrium. The chordae tendineae, however, spring fi papillary muscles, and these are elevations of the wall of the ventricle direc
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Orifice of Nodule Orifice of
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Coronary Artery { Lunule Coronary Artery
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Fig. 626.—Cusps of the Aortic Valve.
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 +
towards the atrio-ventricular orifice. During the wringing movement, theref( of the ventricular wall in systole the papillary muscles, as stated, contract, ; so maintain the chordae tendineae taut, or tightly drawn.
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 +
When the mitral valve opposes the entrance of blood into the left ventr the cardiac affection is known as mitral obstruction (stenosis). When mitral valve is incompetent, and allows regurgitation of blood to take place fi the left ventricle into the left atrium, the cardiac affection is known as mi regurgitation (incompetence).
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 +
The aortic orifice is circular, and is separated from the mitral ori: by the anterior cusp of the mitral valve. It is guarded by the ao; valve, which by means of its cusp prevents regurgitation of bl( from the aorta into the left ventricle during the elastic coil of arterial wall. It is composed of three semilunar cusps or segmei consisting of fibrous tissue, covered on their ventricular surfaces endocardium, and on their arterial surfaces by the endothelial lin of the artery. Each cusp is attached by its convex border to wall of the artery at the place where it springs from the ventri The other border of the cusp is free, and is directed away from ventricle. Each cusp, therefore, is so disposed as to allow the bl<
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THE THORAX
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1063
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)ass freely into the aorta from the left ventricle. The free border
 +
 +
ach cusp is strengthened by a band of fibrous tissue, and at the
 +
tre of the border there is a small swelling, called the nodule [corpus ntii). This gives rise to a slight projection, and on either side of he border is concave. The attached convex border of each cusp Iso strengthened by fibrous tissue. In addition to these fibrous
 +
 +
kenings, fibrous tissue pervades each cusp from the nodule to the
 +
iched border, with the exception of the portions immediately )w the lateral concave parts of the free border. These portions in ti cusp are semilunar, and are called the lunules. They are the mest parts of the cusp, and are transparent, consisting practically udocardium and the endothelial lining of the artery.
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 +
The interior of the wall of the aorta presents three well-marked jsses, each of which is placed opposite a segment of the valve. These isses are called the aortic sinuses (sinuses of Valsalva), and they are dised as anterior, left posterior, and right posterior respectively. The erior sinus presents the orifice of the right coronary artery, and the posterior sinus presents the orifice of the left coronary artery. Each is, together with the corresponding cusp of the aortic valve, forms nail pocket, and the three pockets open away from the left ventricle hat is to say, in a direction corresponding to the normal blood-flow.
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 +
Function of the Aortic Valve— This valve serves to prevent regurgitation of )d from the aorta into the left ventricle during the elastic recoil of the arterial i close to the heart. During the ventricular systole, when the blood is being r en through the aortic orifice, the aortic valve assive, and its three segments are applied to arterial wall. During the elastic recoil of the
 +
 +
rial wall, however, the valve is in action. The
 +
effect of the elastic recoil is to force sufficient
 +
)d backwards towards the left ventricle to close aortic valve. This blood enters the pockets ned by the aortic sinuses and the cusps of the ^e. The cusps are pressed towards the centre of aortic orifice, and they come into contact in following manner: the three nodules come into
 +
 +
e contact at the centre of the aortic orifice, and
 +
dose what would otherwise be a small space, and respective lunules are closely pressed against another. In this manner the aortic orifice is lpletely closed, and regurgitation of blood into left ventricle is in health effectually guarded inst. It will be evident that the strain of the kward pressure of blood must be borne by those tions of the segments which are strengthened fibrous tissue extending from each nodule to attached border of each cusp. Though the ules are thin and weak, nevertheless, being, so to speak, doubled up against ! another, the more they are pressed upon the more closely they fit together. When the aortic valve offers opposition to the entrance of blood into the fa, the cardiac affection is called aortic obstruction (stenosis). On the other id, when the aortic valve is incompetent, and allows regurgitation of blood take place into the left ventricle, the cardiac affection is called aortic regurgiion (incompetence).
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 +
Fig. 627. —The Aortic Sinuses and the Aortic Valves, seen from above.
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 +
The right coronary artery (left in figure) is seen coming from the anterior sinus; the left artery is arising from the left posterior sinus.
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A MANUAL OF ANATOMY
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1064
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The pulmonary valve, which guards the orifice of the pulmon; trunk, is similar to the aortic valve, and the preceding descript is for the most part applicable to it. The cusps of the pulmon; valve are, however, weaker than those of the aortic valve, and 1 sinuses are destitute of any arterial orifices. These sinuses are dispo: as posterior, right anterior, and left anterior respectively.
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The function of the pulmonary valve is similar to that of 1 aortic valve.
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 +
Ventricular Septum. —This septum completely separates the ri^ and left ventricles. The external indications of its attachments ; the anterior and inferior interventricular grooves. It is thick, and for i most part fleshy. It is thickest in the region of the apex, and becon thinner towards the base of the ventricles. It bulges into the ri^ ventricle, so as to be convex on that aspect, whilst it recedes from 1 left ventricle, so as to be concave towards it. The upper or ba part of the septum presents anteriorly a small portion which is destiti of muscular fibres. This portion is thin (see Fig. 621) and consi of fibrous tissue, covered on either side by endocardium.
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It is known as the membranous part of the septum, and is develop from the fused A.V. cushions of embryonic life. It forms the ri^ and posterior part of the wall of the aortic vestibule immediat< below the aortic valves. Its upper part separates the cavity of 1 vestibule from the right atrium, while its lower part is between ventricles', these relations can be seen in Fig. 621.
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Topography of the Orifices of the Heart.-r— The pulmonary orif is situated on a level with the upper margin of the third left cos cartilage at its junction with the sternum. The aortic orifice, whi is more deeply placed than the pulmonary, is situated behind the 1 border of the sternum on a level with the lower margin of the th costal cartilage.
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The tricuspid orifice lies behind the body of the sternum oppos the fourth intercostal spaces and fourth and fifth costal cartilag The mitral orifice, which is placed very deeply, is situated behind 1 left border of the sternum on a level with the fourth left costal cartila The anterior atrio-ventricular groove corresponds with a line dra from the third left to the sixth right costal cartilage, and it is on t line that the two atrio-ventricular orifices are necessarily found.
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Cardiac Bloodvessels—Arteries. —The nutrient vessels of the he are the coronary arteries, right and left, which arise from the root the ascending aorta. For a description of these vessels, see p. 1036
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 +
Veins. —The cardiac veins are as follows: the great cardiac ve the coronary sinus; the posterior cardiac veins; the middle card vein; the small cardiac vein; the anterior cardiac veins; the oblic vein of left atrium; and the venae cordis minimae or smallest card veins. With the exception of the last-named cardiac veins (ve cordis minimae), all the others are seen upon the exterior of the hee
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The great cardiac vein commences at the apex of the heart, 2 ascends in the anterior interventricular groove alongside of the antei
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THE THORAX
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1065
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ventricular branch of the left coronary artery. In this part of its se it is more properly called the anterior interventric.ular vein. of large size, and receives tributaries from both ventricles and the ventricular septum. On reaching the atrio-ventricular ye it enters the left division of that groove, in which it courses y with the left coronary artery. Having turned round the left of the heart, it joins the left extremity of the coronary sinus, which it is continuous. The name coronary, which was sometimes 1 to this vessel, is strictly applicable to it only where it lies in the atrio-ventricular groove.
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Fig. 628. _Heart viewed from below and behind, showing the
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Arterial and Venous Distributions here.
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The coronary sinus is the dilated terminal part of the great cardiac 1. It is about 1 inch in length, and occupies a portion of the terior part of the left atrio-ventricular groove. Its left extremity Dntinuous with the great cardiac vein, and its right extremity opens > the right atrium between the valve of the inferior vena cava and tricuspid orifice, the opening being guarded by the valve of the Dnary sinus. At the place where the coronary sinus is continuous h the great cardiac vein there is a valve, which is composed of two nents.
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The coronary sinus is the persistent left horn of the sinus venosus. The posterior cardiac veins ascend upon the posterior surface of left ventricle, and open partly into the coronary sinus, and partly
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io66
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A MANUAL OF ANATOMY
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into the contiguous portion of the great cardiac vein. One of tl is known as the left marginal vein.
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 +
The middle cardiac vein, which is of large size, commences at apex of the heart, and passes along the inferior interventric groove with the inferior interventricular branch of the right coror artery. It receives tributaries from the adjacent surface of the ri ventricle and from the ventricular septum, as well as a few f: the left ventricle, and opens into the right extremity of the coror sinus.
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Fig. 629. —Diagram showing the Position of the Heart and its Valvl Orifices in Relation to the Anterior Wall of the Thorax.
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R.A. Right Atrium R.V. Right Ventricle L.A. Left Atrium L.V. Left Ventricle A.A. Arch of Aorta In. Innominate Artery
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R.S. Right Subclavian Artery
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R. C.C. Right Common Carotid Artery L.C.C. Left Common Carotid Artery L.S. Left Subclavian Artery
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S. V.C. Superior Vena Cava
 +
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Numbers on Sternum.
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1. Tricuspid Orifice 3. Mitral Orifice
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2. Pulmonary Orifice 4. Aortic Orifice
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The small cardiac vein occupies the right atrio-ventricular gro in company with the right coronary artery, and opens into the ri extremity of the coronary sinus. It is subject to some variat but it usually receives tributaries from the contiguous parts of the ri atrium and right ventricle, including the anterior cardiac veins.
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 +
The anterior cardiac veins ascend on the front of the right ventri and open into the small cardiac vein. One of them is known as right marginal vein.
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The oblique vein of left atrium (oblique vein of Marshall), whic
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a persistent part of the left duct of Cuvier, passes downwards and inw;
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THE THORAX
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1067
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the posterior aspect of the left atrium, and opens into the left emity of the coronary sinus, its orifice being destitute of a valve.
 +
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evelopment. —The oblique vein of left atrium represents the terminal portion e left duct of Cuvier.
 +
 +
rributaries of the Coronary Sinus. —These are as follows: (1) the t cardiac vein; (2) some of the posterior cardiac veins, others of e veins opening into the great cardiac vein; (3) the middle cardiac
 +
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(4) the small cardiac vein; and (5) the oblique vein of left atrium,
 +
h the exception of the last-named tributary, all the others are dded with valves at their terminal orifices, but elsewhere they destitute of valves.
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 +
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 +
Fig. 630. —The Veins of the Heart as seen from in Front.
 +
 +
The heart is supposed- to be semi-transparent.
 +
 +
The venee cordis minimae (smallest cardiac veins) are not visible >n the exterior of the heart. They are very minute, and they open ) the right atrium, their orifices constituting some of the foramina arum minimarum. Similar minute veins are said to open into the atrium, and also into both ventricles.
 +
 +
Lymphatics.—The lymphatic vessels of the heart form two netks—subendocardial and subpericardial. The vessels are ultitely collected into two trunks, right or posterior, and left or erior. The right trunk receives the lymphatics of the right side he heart, and the left trunk takes up those of the left side. Each tik accompanies the corresponding coronary artery, and both pass kwards on either side of the pulmonary trunk. Having pierced pericardium, they terminate in the superior mediastinal or cardiac nds.
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io68
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A MANUAL OF ANATOMY
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Nerves.—The nerves of the heart are derived from the super and deep cardiac plexuses, and through these from the vagus svmpathetic nerves. The branches do the atria are derived p from the deep cardiac plexus, and partly from the coronary plex They form a gangliated plexus on the surface of each atrium her the epicardium, and from this plexus branches proceed to the mus wall. The branches to the ventricles are derived from the right left coronary plexuses. These branches lie upon the surface of ventricle beneath the epicardium, and in the heart of the calf the; readily recognizable as delicate, thread-like streaks. Minute ga are met with at intervals on these nerves in the region of the ba the ventricles, but none on those nerves which lie over the lower thirds of each ventricle. The branches which enter the mus^ substance of the ventricular walls form plexuses, but are dest of ganglia.
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Fig. 631. —The Superficial Muscular Fibres of the Heart in the Region of the Apex (C. Gegenbaur).
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Structure of the Heart. —The cardiac wall is composed of muscular t which is known as the myocardium. This is intimately covered by the vi layer of the serous pericardium, this layer being called the epicardium, an
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cavities of the heart are lined with a mem which is known as the endocardium.
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The epicardium resembles a serous mem in structure, and is covered by endoth( Beneath the epicardium there is a va amount of fat, which is chiefly met with i atrio-ventricular and interventricular groov The endocardium is a smooth, delicate brane, destitute of bloodvessels, and coven its internal surface by endothelium. It co of a connective-tissue basement membram taining elastic fibres, and is continuous th: the arterial and venous orifices with the 1 intima of the vessels. It enters into the f tion of the segments of the atrio-ventricula semilunar valves.
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Fibrous Tissue. — The atrio-ventriculai
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arterial orifices of the heart are each surroi by a ring of fibrous tissue, and these rings, : case of the atria and ventricles, connect them together. The fibrous tiss these rings furnishes that which is met with in the segments of the various v In the triangular interval between the aortic and the two atrio-ventr orifices there is a collection of dense fibrous tissue, of the consistence of cartilage, which is connected with the fibrous rings just referred to, and ' represents the os cordis of the ox. ’When a heart is boiled the fibrous tis dissolved, and the atrial portion can be separated from the ventricular poi Myocardium. —The muscular tissue of the auricles is mostly distinct that of the ventricles, the fibrous rings at the atrio-ventricular orifices vening between the two, and serving to connect them.
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Atria. —The muscular fibres of the atria are arranged in a superfici; common to both atria, and a deep set confined to each atrium. The supe fibres are disposed transversely, and some of them enter the atrial septum, are best marked in front. The deep fibres are arranged in two sets, loope< circular. The looped fibres arch vertically over the atrium, their extrei being attached to the ring of fibrous tissue which surrounds the atrio-ventr orifice. The annular fibres are present in the auricle around the venous or and around the fossa ovalis. The walls of the atria, though muscular, are
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The whorled arrangement is well shown.
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THE THORAX
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1069
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ntricles. —The muscular fibres of the ventricles are, as stated, mostly
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t from those of the atria, and are disposed in a very complicated manner,
 +
spring for the most part from the rings of fibrous tissue which surround trio-ventricular orifices. The superficial fibres descend obliquely towards jex, where they are disposed in a twisted or whorled manner, after which pass on to the inner surface of the left ventricle. Some of them become iuous with the papillary muscles of that ventricle, whilst others ascend as
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ical layer on the inner surface of the ventricle to be attached to the left
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 +
632. —Anterior View of Heart of a Young Subject dissected after Long Boiling, to show the Superficial Muscular Fibres (Allen Thompson), f. (From Quain’s ‘ Anatomy.’)
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figure is planned after one of Luschka’s, but its details were chiefly taken from an original preparation. The aorta, b', and pulmonary trunk, a', have been cut short close to the arterial (semilunar) valves, so as to show the anterior fibres of the atria; a, superficial layer of the fibres of the right ventricle; b, that of the left; c, c, anterior interventricular groove; d, right atrium; d' , its auricle, both showing chiefly perpendicular fibres; e, upper part of the left atrium; between e and b ', the transverse fibres which behind the aorta pass across both auricles; e', auricle of left atrium; /, superior vena cava, around which, near the atrium, circular fibres are seen; g, g / , right and left pulmonary veins with circular bands of fibres surrounding them.
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)-ventricular fibrous ring. The superficial fibres are common to both
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xicles.
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the remaining fibres are very numerous, and must be described separately -ach ventricle. The principal fasciculi of the left ventricle spring from the atrio-ventricular fibrous ring, and they pass more or less obliquely towards apex. In their course they turn inwards, and enter the front part of the Ticular septum interiorly. Some of them now pass upwards to the base of ventricle to be attached to the collection of dense fibrous tissue, of the conTice of fibro-cartilage, already described; others pass across to the posterorior wall of the right ventricle, where they partly end in a papillary muscle,
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1070
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A MANUAL OF ANATOMY
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and partly pass to be attached to the right atrio-ventricular fibrous ring; i a third set pass to the postero-inferior wall of the left ventricle, where become circular in direction. The principal fibres of the right ventricle are the superficial fibres, continuous with those of the left ventricle, and spring the fibrous rings around the atrio-ventricular and pulmonary orifices. ' on the postero-inferior surface of the right ventricle pass into the ventr: septum, and having traversed it obliquely forwards and upwards, they from it, and become continuous with the deep fibres of the left ventricle. r on the sterno-costal surface of the right ventricle also pass into the ventr: septum, and having traversed it obliquely backwards and downwards, they on to the postero-inferior wall of the left ventricle. Those from the in aspect of the right ventricle enter the lower part of the ventricular septum
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sino-atriai node
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Fig. 633. —The Sino-atrial Junction (after Tandler).
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ascend in the septum to the collection of dense fibrous tissue of the consisten fibro-cartilage at the base. Although the ventricular muscular fibres are disj for the most part obliquely, there are some annular fibres, but these are con to the thickest part of each ventricular wall.
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Fibres of Purkinje. —These fibres are situated between the endocardium the cardiac muscular tissue. They consist of elongated cells united at their so as to form chains. The central part of each cell contains granular protopl within which there are two nuclei; and the peripheral part presents trans 1 striations. These cells are probably vestiges of an early condition of ca; muscular fibres.
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Sino-atrial Node. —In the region of the sulcus terminalis is a small oval (Fig. 633) measuring about 10 mm. in length and from 3 to 5 mm. in w where the muscular fibres are arranged so as to form a delicate network
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THE THORAX
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1071
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■atrial node or the node of Keith and Flack. It is believed to be the spot
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e the contraction of the heart begins and from where the wave of contraction
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eeds over the heart.
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Ltrio-ventricular Bundle (Figs. 634 and 635).—This bundle constitutes the atrio-ventricular muscular connection, and functionally is of a conducting ire. It begins in the atrio-ventricular node, which is situated in the central >us body of the heart a little below the opening of the coronary sinus into right ventricle. The node consists of an intricate network of muscular fibres rmingled with, and embedded in, fibrous tissue. Entering the node are
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Sup. Vena
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Fossa Ovalis
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Ascending Aorta
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ve of Inferior ena Cava
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^alve of anary Sinus
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if. Vena Cava
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rio-ventricular Node
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Right Fasciculus of Atrio ventr. Bundle
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Pulmonary
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Artery
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Moderator Band
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Right Ventricle
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634-—The Atrio-ventricular Node and the Right Fasciculus of the Atrio-ventricular Bundle as seen from the Cavity of the Right Ventricle (after Tandler).
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es of an indefinite but probably atrial origin. From it proceeds a single die, which represents the main stem of the atrio-ventricular bundle. This n passes forwards along the upper margin of the muscular portion of the tricular septum, lying immediately below the membranous part, and beneath anterior part of the base of the medial cusp of the tricuspid valve. In this ation the main stem breaks up into two fasciculi—right and left. Each of these aculi enters the septal wall of the corresponding ventricle, and divides into nches which ramify beneath the endocardium, where they form part of the tern of Purkinje’s fibres. Ultimately the terminal ramifications blend with muscular fibres of the ventricles and papillary muscles. A slip from the
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1072
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A MANUAL OF ANATOMY
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right fasciculus passes to the anterior papillary muscle of the right vent] within the moderator band. To open this band and discover the slip is perl the simplest way of exposing the bundle.
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The fibres of the atrio-ventricular bundle are pale, and are furnished i nerve-fibres and ganglia. The clinical significance of the bundle has refert to Stokes-Adams disease, or heart-block.
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Structure of the Cardiac Valves. —Each segment of the tricuspid and m valves consists of two layers of endocardium, enclosing between them fib tissue which is derived from the fibrous ring around the corresponding a ventricular orifice. Each segment of the aortic and pulmonary valves
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Em. 635.— The Left Fasciculus of the Atrio-ventricular Bundle
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SEEN ON THE VENTRICULAR SEPTUM FROM THE CAVITY OF THE L
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Ventricle (after Tandler).
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consists of two layers of endocardium, enclosing between them fibrous tis which is derived from the fibrous ring around the corresponding arterial orif The segments of all the-valves are destitute of bloodvessels.
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Minute Structure of the Myocardium. —Cardiac muscle is composed of tra versely striated fibres, but these differ so much from ordinary striated volunt muscular fibres as to require a special description. They possess no sarcolemr they branch freely, and adjacent branches unite, so that an intricate netw< is formed by them, and the transverse strias are fainter and less regular tl those of voluntary muscle. Each fibre and its branches are broken up inti series of short quadrangular muscle corpuscles, arranged in rows or chains, 2 separated from one another by cross-marks. Each muscle corpuscle conta
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THE THORAX
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1073
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ucleus, which occupies the centre of the corpuscle, and the corpuscle presents tudinal striae as well as transverse. A cardiac muscular fibre, as well as anches, is therefore a chain of muscle corpuscles, each of which has a nucleus centre, and there is an absence of sarcolemma. height of the Heart. —The average weight of the
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of the adult male is 10^ ounces, and of the adult
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le 8 |- ounces.
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ize. —The size of a normal heart has been compared ie closed hand of the individual person, development of the Heart. —In the absence of definite mation, the human heart must be considered as ig primarily from the fusion of vessels in the edges Le advancing mesoderm in the protocardiac area of embryonic plate. Moreover, these vessels must be ned to lie in the visceral portion of this mesoderm,
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>ugh the presence of a pericardial split at such an ' stage is doubtful; thus the heart would be in assoDn with the roof of the yolk-sac, and, when reversal 3 place, with the floor of the fore-gut, to which it would
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tached by its mesodermal covering. The single tube
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ting from the fusion enlarges rapidly, standing away . the roof of the pericardium, and drawing after it Ding so a dorsal mesocardium, which ' suspends ’ it . the roof. The existence of a ventral mesocardium sry doubtful; if it does occur, it disappears at an edingly early stage.
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'he single-looped cardiac tube formed in this way nds forward from the septum transversum, where its er end is continuous with the sinus venosus, which is into it. Its anterior end turns up as the aortic or rial stem or truncus arteriosus, entering the mesolal floor of the fore-gut, where it divides. The true iac tube, lying between these two fixed extremities,
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. shows three primary dilatations, or primitive (single) chambers—the atrium Fig. 638), into which the sinus venosus opens directly; the ventricle (V); the bulbus cordis (B), from which the aortic stem issues. The dorsal mesoium, seen in the figure, disappears in its central area very quickly, thus
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Fig. 636. — Cardiac Muscular Fibres,
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SHOWING THEIR
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Transverse Stride, Divisions, Junctions, and Position of the Nuclei.
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• 637. —Scheme showing Four Successive Stages in the Development of the Heart (F. Testut’s ‘ Anatomie Humaine ’).
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x. Arterial Bulb. 2 . Ventricle. 3* Atrium.
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4. Veins opening into the Sinus Venosus.
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dng a passage from one side to the other dorsal to the heart, and between arterial and venous ends; this is the transverse sinus of the adult perilium.
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Sections through the heart show at this and succeeding stages that an inner ocardial tube forms a cellular structure, separated by a subendocardial
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68
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io 7 4
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A MANUAL OF ANATOMY
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space from an outer myocardial tube of contractile mesoderm cells. The sp is occupied by subendocardial fluid, probably contained in greatly disten< cells; it is invaded later by the growing myocardium, on which the endocan layer is then laid, the result being the intracardiac network characteristic of true cardiac tube. The three parts of the cardiac tube enlarge rapidly, atrium and ventricle particularly, the result being, as shown in the sec( diagram in the figure, that the bulbus is now directed backwards as well upwards, the large atrium is beginning to lap round it on each side from behi and the ventricle is situated ventrally between the two. Other results also fol this rapid growth; the sinus venosus is gradually drawn into the pericardial ca\ at the venous end, and the truncus arteriosus—though not nearly to so gr a degree—at the arterial end.
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Fig. 638. —Schematic Figures of Early Heart.
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In the first the heart tube is shown from the left in the pericardium (P), and 1 a single atrium (A), ventricle (V), and bulbus (BC). Opening into it behi is the sinus venosus (SV) embedded in the septum transversum above a in front of the liver-bud. A complete dorsal mesocardium (DM) is prese: this quickly breaks through and disappears in the dotted area. The secc figure shows the effect of growth of the tube without corresponding incre; in distance between its terminal attachments. The third diagram illustra the positions in the bent tube assumed by the dorsal (D) and ventral ( cushions in the A.V. and arterial regions. R, L, are right and left venc valves beside the opening of the sinus venosus.
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The tube is narrowed into an atrio-ventricular* canal between the dilal atrium and ventricle, and here endocardial cushions (A . V. cushions) are ma (by the subendocardial tissue), which partly block the passage of the A.V. can dorsal and ventral cushions are formed first, right and left, smaller ones being add later. At the aortic orifice arterial cushions are similarly produced rather m< slowly. All these structures are concerned in the development of valves.
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In the fourth week the heart, seen from the front, presents a surface appe; ance such as is shown in Fig. 642. Some of the parts of the adult heart can recognized here in a rudimentary state, but the cavity within is still undivid being a single passage from venous to arterial end. The division into ri£ and left passages must now be described; it is convenient to take the cavit
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Frequently written A.V. for brevity.
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THE THORAX
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1075
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itely, but it should be underthat the division goes on in rious parts more or less at the time.
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Atrial Septa and Atria. —As
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nus venosus is drawn out into ericardium from the septum rersum, its opening into the 1 is found to be no longer in, but on the right of the e line; this is probably due ferences in growth-rate of the des of the atrium. The opento the atrium is. guarded by s valves, right and left. As the a enlarges, a septum primum rs as a falciform edge (Fig. 640) ig round the upper wall of the r a little to the left of the left s valve. It quickly extends
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the front and back walls, mg in this way the upper and
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A.V. endocardial cushions, large interatrial opening enI by this septum above the )ns is the foramen primum. septum becomes deeper (Fig. and the foramen primum is ately closed by the meeting of the free edge of the septum with the A. V. cushions ; efore this occurs a foramen secundum appears as the result of breaking
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g. 640. —Hearts of Embryos of 4-5 Mm. and 10 Mm. respectively.
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t wall of right atrium cut away in each case to show deepening of septum )rimum (S. I.); F.i, foramen primum; F.2, foramen secundum; S.V., anus venosus. Venous valves are not shown.
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gh of the upper part of the septum. This is seen at an early stage in the d figure in Fig. 640.
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Fig. 639.—Section through Cardiac Tube in 2-5 Mm. Embryo, showing Endocardial Tube (E), Subendocardial Space (S), and Myocardial Tube (M).
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A MANUAL OF ANATOMY
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1076
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The septum secundum* develops as a low, falciform, and fairly thick e on the upper wall a little distance to the right of the first septum, and after foramen secundum has appeared. Its lower and posterior end runs into left venous valve—which is not shown in Fig. 640—and its anterior end is on the upper and front wall. It overhangs the foramen secundum on the ri It increases very slightly in height, but its anterior end, extending round front wall, reaches the dorsal A.V. cushion here, and becomes continuous 1 the lower end of the joined venous valves; it will be noticed again with t! and it is only necessary to say here that it forms the annulus ovalis.
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The opening of the sinus venosus, guarded by its two venous valves, li little to the right of the septal structures low down on the posterior wall, two valves, projecting into the atrial cavity, are joined above and prolongec the wall as an upper fornix; owing to the shortness of the left valve, thei no proper lower fornix. The upper fornix, large and developed early, t forward along the upper wall, and is lost on the upper front wall; it mak prominent edge, sometimes referred to as the ‘ septum spurium.’
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The lower fornix, or, more truly, the lower end of the right valve, reaches hinder or ventralf A.V. cushion. The space on the back and upper walls, betv the septum primum and the sinus valves and upper fornix, is known as intersepto-valvular space ; the septum secundum projects into this from abo
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The dorsal and ventral A.V. cushions fuse during the sixth week, divi< the A.V. canal into right and left channels. When this occurs, the lower fo extends and reaches the lower front end of the septum secundum, which has 1 seen to have reached the dorsal cushion.
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The opening of the sinus into the atrium gets larger, the right valve stre ing out towards the right, the left coming against the septum primum obliterating the lower part of the intersepto-valvular space; it degener here, but some remnants of it may be found on the septum. The right v; forms the valve of the inferior vena cava, attached below and in front to remnant of the septum secundum, and being lost above and behind as the remr of the upper fornix, the crista terminalis . The enlargement is associated a the increasing size of the opening into the sinus of the inferior vena cava schemes in Fig. 641).
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It is really the right horn of the sinus venosus that is engaged in this enla ment, which makes it become a part of the right atrium, that part into w] the venae cavae open; the original atrial cavity on this side is pushed outw by its enlargement, and forms only the auricle. The left horn of the s: venosus, forming the coronary sinus, , becomes descriptively only a seconc vessel opening into the large right horn, and the spur between the opening the two horns, at first some distance from the atrium, comes up (Fig. 641 its level, and finally becomes the part of the valve of the inferior vena cava 1 lies between the openings of the coronary sinus and inferior vena cava; corresponding part of the right venous valve makes the valve of the coroi sinus, as in the figure.
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Thus the right atrium of the adult heart is developed from the right 1 of the sinus venosus so far as its atrium is concerned, the original atrium ( forming the auricle. The valve of the inferior vena cava is formed from right venous valve and the spur between the horns, the valve of the coronary s\ from the lower part of the right valve, and the septum is a compound of sep primum (septum ovale) and septum secundum (annulus or limbus ovalis).
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The foramen ovale (foramen secundum) usually remains patent to a si extent for many years.
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Two distinct structures seem to be confused in the descriptions givei
 +
this septum. One is apparently only the upper remnant of the septum prm above the secondary foramen; the other is the one described here, and app< to be in reality the proper septal structure between the left and right sides. :
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f The nomenclature of these cushions, as seen from the auricular aspect, be understood from the third diagram in Fig. 638.
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THE THORAX
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io 77
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e cavity of the left atrium is produced in a somewhat similar manner. A common pulmonary vein, made by junction of right and left branches, ad opening into the left atrium at the end of the first month close to the n primum. It gradually enlarges, increasing in diameter, but not pronately in depth. Thus its right and left branches come to open into a r which, by its increase in diameter, is pushing the original atrium away ds the left. Still enlarging, the venous cavity takes up its right and left hes into itself, thus leading to their next two branches on each side coming
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. 641. —First Figure: Atrial Cavities exposed by Removal of the Upper and Front Wall in an Embryo of 4-5 Mm.
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atrio-ventricular opening; RVV, right venous valve, marking off sinus enosus, into which common cavity open the right and left horns of the inns (RHSV, LHSV). The left venous valve is not yet formed. The smaining figures, semi-diagrammatic, show the taking up of the sinus ito the atrium; the right atrial wall only is removed, leaving the septum rimum (SEPT. I.) in position, with the foramina (FOR. I. and II.) above nd below it. ISVS, intersepto-valvular space; LVV, left venous valve; VC, opening of inferior vena cava.
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2n directly into the cavity. In this way the atrium is made from dilated inary veins, the auricle representing the original true atrium. ie A.V. canal, as already said, is divided into right and left A.V. openings e fusion of the dorsal and ventral endocardial cushions. The persisting ires are guarded by right and left cushiohs, with the corresponding ends ! fused central pair. The fusion occurs about the sixth week, and about ime time the foramen primum closes on their atrial aspect, and the venir septum is nearing its completion on their other side.
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Ventricles and Bulbus Cordis.— In Fig. 642 the 4-5 mm. heart is viewed the front, and the common ventricle is seen to bulge somewhat to the ying to the left of the bulbus, and on the whole rather below it. The
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A MANUAL OF ANATOMY
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1078
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companion drawing shows this heart with the front wall removed fror ventricle and bulb; the cavities of these two parts are seen to be separated j by a prominent bulbo-ventricular ‘ spur ’ or angle, which, by its presence, c the opening into the bulb to lead out of the right extremity of the ventr: cavity to the right, in front of, and rather below the atrio-ventricular ape: This aperture is seen guarded by its endocardial cushions.
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The ventricular cavity is already showing an early state of division right and left ventricles, for a low septum is visible extending back to the in
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Fig. 642. —Views from the Front of Hearts of Embryos of the Fo and Fifth Weeks (4*5 Mm. and 10 Mm.) (from Reconstructions)
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On the right are shown the interiors of these hearts, the front walls of the tricles and bulbs, and to some extent of the atria, having been rem< l.a., l.v., left auricle and ventricle; r.v., right ventricle; r.b.r., right b ridge; art. cush., endocardial cushions at beginning of arterial trunk; sept., interventricular septum.
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A.V. cushion. This septum is really little more than the original floor o cavity persisting at its original level, the two subdivisions of the cavfh larging downwards on each side of it. Thus the right ventricle starts existence as a bulging of the common ventricle; this bulging can be seen oi surface view of the heart.
 +
 +
Turning now to the 10 mm. embryo (Fig. 642), it is to be noticed tha bulbo-ventricular spur has decreased much in prominence; this is due to a atrophy and disappearance, so that the bulbar opening is now above the
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THE THORAX
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1079
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e right-hand end of the A.V. aperture. The ventricles have become deeper the septum proportionately higher, but that the septum has not grown ird is evident from the fact that it retains its old level of attachment to the - A.V. cushion.
 +
 +
t the 15 mm. stage (not shown) the process of reduction of the bulboicular angle has gone even farther, the whole left and back wall of the having practically disappeared, so that the arterial cushions are, in this very near to the A.V. cushions. At the same time the greater part of the opening is, as a result, now brought directly under the passage into the ining bulbus.
 +
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urning back to the 10 mm. specimen (Fig. 642), certain changes within >ulb itself are to be seen. These consist in the development of two bulbar S. The right ridge is seen almost entire; it begins above just below the ial cushions (with the right one of which it is continuous), and passes down back on the right bulbar wall, to end in a blunt extremity just to the right
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 +
 +
 +
Fig. 643.—To show Method of Division of Bulbar Region and
 +
 +
Formation of Aortic Vestibule.
 +
 +
(Explanation in text.)
 +
 +
le A.V. opening. The left ridge starts below the left lateral aortic cushion, extends downwards and forwards on to the left front wall of the bulbus, his part has been cut away in the figure, the ridge is only partly seen cut ss. These two bulbar ridges thus overhang a deep channel, which can be in the figure, traceable downwards and to the left towards the left ventricle, each which its groove would be continued in front of the A.V. cushions and ve the edge of the ventricular septum, ihis channel becomes the aortic inel, or aortic vestibule of the complete heart, closed in, as will be described, he fusion of the ridges with each other, and with the edge of the septum.
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In the 15 mm. stage, when the spur and the associated bulbo-ventricular - on the surface have disappeared, the atrophy affects mainly the wall of the 5 behind and below the left ridge, but this is nevertheless shorter than the t ridge, thus exhibiting the general tendency to shortening of this region.
 +
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complete division of the bulbar region and separation of the two ventricles
 +
1 follow; the way in which this happens is schematically shown in Fig. 043.
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io8o
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A MANUAL OF ANATOMY
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In these schemes the front wall of the right ventricle only is supposed to ] been removed with that of the bulb, so that the interventricular septum (w in the previous figures has only been seen in part) is now seen as a whol< not only reaches the lower A.V. cushion, but runs into the upper cushion corresponding situation, making a free falciform edge between these two po The free edge forms the boundary of the interventricular foramen, the d( wall of which is made by the cushions. The dorsal and ventral cushions j leaving now two lateral atrio-ventricular openings, one on each side of the p of the septum and interventricular foramen. In the first diagram the bulbar ridge is seen at a and the right at b\ these are continuous above 1 the left (/) and right (r) arterial cushions respectively; these cushions are fn so that a pulmonary orifice [pa) is between them and the ventral cushion
 +
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Fig. 644.—Bulbo-ventricular Region (15 Mm.).
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The first figure shows the bulbar ridges in position, the second shows the ao channel, the ridges and parts of the walls being cut away. S, upper of interventricular septum; A, the fused (lateral) arterial cushions; D, dorsal arterial cushion.
 +
 +
The two small figures show how the septum between aorta and pulmon artery meets the fused lateral arterial cushions, leaving three semilu rudiments to each artery. D, V, dorsal and ventral cushions.
 +
 +
The second plan shows how the descriptive position of the definite cr results from a small amount of rotation from right to left.
 +
 +
and separated by these from the aortic orifice, which lies between them and dorsal cushion. The aortic orifice leads into the aortic channel (ao), wh overhung by the bulbar ridges, passes downwards and to the left in front of A^V. cushions, and through the interventricular foramen into the left ventri When fusion occurs between the A.V. cushions it affects those parts that m the floor of the aortic channel— i.e., the cushions bounding the transv( sht and the upper part of the right lateral slit—leaving the lower part (av) the right lateral slit as the permanent right opening.
 +
 +
In the second diagram the mode of closure is illustrated. The right bul ndge grows towards the left across the right lateral A.V. orifice—between closed and unclosed parts—and just reaches the attachment of the ventrici septum to the lower cushion. The left ridge, in contact from its early st;
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THE THORAX
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1081
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the upper part of the septum, begins to extend along the free margin of this ; dent of its growth along this margin is indicated by the dotted line. The idge in this way reaches the right ridge by growth along the edge of the ventricular foramen, and by fusion between the two ridges the aortic channel fed in and separated from the (right) cavity continuous with the pulmonary 3. In the third figure the actual conditions (a little simplified) are shown embryo of the sixth week, in which the various parts are in the process iction and consolidation; it may be noted that a certain amount of extension sue from the fused arterial cushion takes place between the upper parts 3 two bulbar ridges.
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Dr descriptive purposes the dorsal wall of the bulbar region has been given rth in the figure greater than it really possesses; owing to the disappearance 3 left dorsal wall with the bulbo-ventricular spur, the dorsal arterial cushion ictically next to the A.V. cushions, so that the ' floor ’ of the aortic channel >elow the aortic orifice is made by the fused A.V. cushions; this is the memus part of the ventricular septum, separating the aortic channel (aortic Dule) from the right atrium. The ventral wall of the aortic vestibule is made le fused bulbar ridges, and it is evident that the interventricular foramen, ugh it no longer affords a passage between the left and right ventricles, sts as the opening into the aortic vestibule (from the general cavity of the ventricle) to the right of the left A.V. orifice. The remnants of the A.V. ons, presenting as pouting lips in the ventricular cavities, and continuous
 +
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with the endocardial covering of the muscular network of the ventricles,
 +
ne atrio-ventricular valves, modification in the network producing the chordce yiece and papillary muscles. On the left the cushion lips are placed vertically e the vertical slit, and the two valves derived from them lie naturally een the opening and the aortic vestibule and the left marginal wall respecy On the right the vertical lips (Figs. 643 and 644) separate the orifice from ieptum and the right marginal wall respectively, but in addition there is a >verse flap derived from (or in association with) the right bulbar ridge e this crosses the line of the orifice, and this flap separates the orifice from Dulmonary channel, and hence becomes the anterior (infundibular) cusp. umming up the description given of the formation of the parts, it may be that the infundibulum is a remnant of the bulbus cordis, but its dorsal wall oduced by fused bulbar ridges; the cavity of the aortic vestibule is also a part lat of the bulbus, with an added * ventricular ’ part brought into existence he disappearance of the bulbo-ventricular spur; the membranous part of ventricular septum marks the position of fused A.V. cushions, the interricular foramen remains as the opening into the aortic vestibule from the ral cavity of the left ventricle; and the A.V. valves are derived from the cushions, the anterior cusp of the right valve being an additional structure lected with the growth of the right bulbar ridge.
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Tie arterial (semilunar) valves are developed by hollowing out of their arterial ices from the arterial cushions already mentioned. These are four m number
 +
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ht and left lateral, dorsal, and ventral. The lateral cushions fuse, coning the single orifice into two—ventral or pulmonary, and dorsal or aortic,
 +
division of the bulbar region below these cushions has been described, and bulbar ridges which make the dividing wall have been seen to be continuous se with the fused lateral cushions; in a similar way the dividing wall between two arteries above them is continuous with the fused lateral cushions. I he arteries become completely separated, the separation extending through valvular region, and incompletely involving the bulbar region, thus the original cushions are divided (Fig. 645) into six, three for each orifice, these are hollowed into the arterial valves; the pulmonary orifice has the tral flap and two postero-lateral, the aortic opening has two antero-lateral the dorsal flap. Towards the end of intra-uterine life, however, the heart ergoes a rotation from right to left to such an extent as to place the root o pulmonary trunk in front and to the left of the root of the aorta. 1 he a, as well as the pulmonary trunk, is involved in this rotation, and the seg
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1082
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A MANUAL OF ANATOMY
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ments of the pulmonary and aortic valves are now permanently alterec position. The relations of the various segments in the adult are as folic the cusps of the pulmonary valve are disposed as two anterior, right and : and one posterior ; whilst the cusps of the aortic valve are one anterior and posterior, right and left.
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Fig. 645.— Schemes to show Formation of Arterial Valves froi
 +
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Arterial Cushions.
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A, P, ventral and dorsal cushions. The second scheme shows the division
 +
 +
the four cushions into six. The third scheme shows the effect of rctai
 +
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on the descriptive positions of the valves.
 +
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The rotation just referred to also explains why the left ventricle of the ac heart is chiefly postero-inferior in position, comparatively little of it appeal on the sterno-costal surface of the adult heart.
 +
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Peculiarities of the Foetal Circulation. —The structures peculiar the foetus in connection with the circulation of the blood are follows:
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1. Foramen ovale. 4. Umbilical arteries.
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2. Valve of the inferior vena cava. 5. Umbilical vein.
 +
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3. Ductus arteriosus. 6. Ductus venosus.
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The foramen ovale is an oval opening in the atrial septum, to the fourth month of intra-uterine life it is quite free, but af that period the valve of the foramen ovale gradually extends upwai on the left side of, and beyond, the annulus ovalis, and acts as a val during the latter months of foetal life. The blood can then only fl from the right atrium into the left, its return being prevented this valve.
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The valve of the inferior vena cava is of large size during foe
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life, and is associated with the orifice of the inferior vena cava at 1 postero-inferior angle of the right atrium. It is a crescentic fold of t endocardium, which extends between the anterior margin of t orifice of the inferior vena cava and the anterior horn of the annu. ovalis. Its situation is such as to direct the blood entering the ri£ atrium by the inferior vena cava to the foramen ovale.
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The ductus arteriosus connects the pulmonary trunk to the ai of the aorta at a point immediately beyond the origin of the 1
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THE THORAX
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1083
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Flavian artery, and conveys most of the blood from the right
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ricle to the descending thoracic aorta.
 +
rhe umbilical arteries (hypogastric arteries), right and left, are proved from the common iliac arteries to the umbilicus, through which ) leave the body of the foetus, and pass along the umbilical cord >e distributed to the foetal part of the placenta. They convey the ure blood of the foetus to the placenta.
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rhe umbilical vein extends from the foetal part of the placenta >ugh the umbilicus to the inferior surface of the liver, where it joins left branch of the portal vein. After parting with its right and left aches the umbilical vein is prolonged, under the name of the tus venosus, to the inferior vena cava, which it joins at the fossa vena cava of the liver. The umbilical vein conveys pure blood n the placenta into the body of the foetus.
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Foetal Circulation.— The right atrium receives blood from the erior and inferior vense cava 4 , and from the coronary sinus. The erior vena cava returns the venous blood from the head and neck, upper limbs, and the thoracic portion of the trunk; and the inferior 1a cava returns the blood from the lower limbs, the abdominal tion of the trunk, and the placenta. The placental blood is pure, l reaches the inferior vena cava in two ways: (1) a large quantity it is conveyed directly into the inferior vena cava by the ductus iosus; and (2) some of it circulates through the liver in the branches the portal vein, and is then conveyed to the inferior vena cava by i hepatic veins. The blood entering the right atrium by the inferior 1a cava is necessarily of a mixed nature, being partly placental and
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tly venous.
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The impure blood which enters the right atrium by the superior la cava, having received a small quantity of the mixed blood which
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ers by the inferior vena cava, passes through the right atrioitricular orifice into the right ventricle, and from thence is driven
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0 the pulmonary trunk. A small quantity of it is conveyed to the lgs by the right and left pulmonary arteries, which at this peiiod j of small size, and it is returned from the lungs to the left atrium the pulmonary veins. By far the greater part of the right ventricular )od, however, enters the ductus arteriosus, and is con\eyed by it the aorta immediately beyond the origin of the left subclavian artery. >ne of this blood, therefore, enters the three great vessels which ring from the arch of the aorta. The whole of it descends in the scending thoracic and abdominal portions of the aorta, and has a ofold destination. Part of it is distributed to the abdominal and lvic viscera, and the lower limbs, whence it is returned by the »rtal vein and inferior vena cava; but the greater part of it is conyed out of the bodv of the foetus to the placenta by means ot the nbilical arteries. Having been purified in the placenta, it is returned ence by the umbilical vein into the body of the foetus. This placental ood, as stated, reaches the inferior vena cava in two ways. P ar t y rectly by means of the ductus venosus, and partly indirectly by
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1084
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A MANUAL OF ANATOMY
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means of the hepatic veins after having circulated through 1 liver.
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A small quantity of the mixed blood which enters the right atrii by the inferior vena cava mingles with the venous blood which ent that cavity by the superior vena cava; but by far the greater part it is directed by the valve of the inferior vena cava to the forarr ovale, through which it passes into the left ventricle. Here it recen the blood which has been returned from the lungs by the pulmom
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Internal Jugular Vein Common Carotid Artery
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\fi/ o
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Subclavian Vessels
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Superior Vena Cava
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Foramen Ovale Orifice of Inferior Vena Cava
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Valve of Inferior Vena Cava Inferior Vena Cava
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Ductus Arteriosus Pulmonary Artery
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Left Auricle
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Left Ventricle
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Hepatic Veins
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Aq-Right Ventricle
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Inferior Vena Cava Aorta
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Common Iliac Vein
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External Iliac Vessels
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Ductus Venosus
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Left Branch of Portal Vein
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— Right Branch of Portal Vein
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-Portal Vein
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Umbilical Vein Umbilicus
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— Umbilical Arteries - Umbilical Vein
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Umbilical Cord
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Umbilical Arteries
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Fig. 646. —Diagram of the Organs of Circulation in the Foetus The arrows indicate the course of the circulation.
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veins, and then it passes through the left atrio-ventricular orifice ir the left ventricle. From the left ventricle it is driven into the aou and the greater part of it passes into the innominate, left comm carotid, and left subclavian arteries, to be distributed to the bra head and neck, and upper limbs, as well as to the substance of the he£ by the coronary arteries. A small quantity, however, of this mix blood passes into the descending thoracic aorta, and mixes with t venous blood entering by the ductus arteriosus. The blood is return to the right atrium of the heart from the brain, head and neck, ai
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THE THORAX
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1085
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sr limbs, by the superior vena cava, and from the substance of heart by the coronary sinus.
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Changes at Birth.—At birth respiration is established, and the rs perform their respiratory function; the right and left pulmonary ries undergo rapid enlargement; and the placental circulation is rely arrested. The umbilical arteries become obliterated and Lsformed into fibrous cords, except at their. roots, where they list as the internal iliac arteries. The umbilical vein becomes terated, and is now known as the ligamentum teres of the liver. ductus venosus becomes transformed into a fibrous cord, called ligamentum venosum, which occupies the fissure of that name in liver. The foramen ovale is closed by the valve of the foramen \e becoming adherent to the margin of the annulis ovalis on its left i. In some cases, however, this union is incomplete, and a minute ning persists, through which a small probe may be passed. In y rare cases a fairly large opening may remain, as in the condition ,wn as morbus cceruleus. As viewed from the interior of the left urn, the upper crescentic border of the valve of the foramen ovale isible upon the atrial septum, and above this border there is a slight session. The ductus arteriosus becomes obliterated, and persists a fibrous cord, called the ligamentum arteriosum, which passes n the root of the left pulmonary artery to the arch of the aorta nediately beyond the origin of the left subclavian artery.
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The closure of all the peculiar structures associated with the
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al circulation is usually complete from the eighth to the tenth day
 +
er birth.
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Trachea in the Thorax.—dhe thoracic portion of the trachea extends m the level of the upper border of the manubrium sterni to the el of the intervertebral disc between the bodies of the fourth and h thoracic vertebrae, where it divides into the two bronchi, right and 1. It occupies a median position in the superior mediastinum, and length is about 2 -| inches. As in the neck, it is cylindrical and n in front and at the sides, but posteriorly it is flattened and mem mous, where it rests upon the oesophagus. . .
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Relations— Anterior. —The manubrium sterni, and the origins ot 3 sterno-hyoid and sterno-thyroid muscles; the remains of the ymus; the origins of the innominate and left common carotid series, and the left innominate vein; and the arch of the aorta, which s upon it immediately above its bifurcation into the two bronchi, th the intervention of the deep cardiac plexus of nerves. R° s ~ ior. —The oesophagus, which in an upward direction inclines rtially to the left of the trachea. Right. —The right vagus nerve; e innominate artery after it has left the front of the trachea, and e right pleural sac. Left. —The arch of the aorta and the e mmon carotid artery after these have left the front of the trachea, e left subclavian artery; and the left recurrent laryngeal nerve. Bronchi.—The bronchi, right and left, commence at the bifuica>n of the trachea, and each passes to the hilum of the coriespond
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io86
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A MANUAL OF ANATOMY
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ing lung, where its ramifications commence. As in the trad each bronchus is cylindrical and firm in front and at the sides, posteriorly it is flattened and membranous. There being cerl differences between the bronchi, a separate description is requi for each.
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The right bronchus is about i inch in length up to the point wf it gives off its first, or eparterial, branch. It has about six ca laginous rings, and is larger than the left bronchus. It is more vert:
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than the left bronchus,
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Epiglottis
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Greater Horn of Hyoid Bone Lesser Horn of Hyoid Bone
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Body of Hyoid Bone —
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Thyro-hyoid Membrane - Levator Glandulae \ Thyroides Muscle /
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Thyroid Cartilage -Crico-thyroid Ligament
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Pyramid ” Cricoid Cartilage " Lateral Lobe of Thyroid Gland Isthmus
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Right Bronchus Eparterial Bronchus,
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Hyparterial Bronchus.^
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Trachea
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Left Bronchus
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Fig. 647. —The Hyoid Bone, Larynx, Trachea, Bronchi, and Thyroid Gland (Anterior View).
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therefore coincides with direction of the trachea t greater extent than its felL
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Relations— Superior .—" vena azygos arches over it open into the superior v< cava. Posterior. —The ri{ vagus nerve.
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About 1 inch from commencement the rij bronchus gives off a brar from its outer side wh passes to the upper lobe the right lung. This brar is known as the eparter bronchus, because it ari; above the right pulmonc artery. The rest of the ri£ bronchus is spoken of as bei hyparterial.
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The left bronchus is abc
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2 inches in length. It I about twelve cartilaginc rings, and is smaller than t right bronchus on account the smaller size of the 1< lung. Its course is more c lique than that of its fello
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and it is directed downwards and outwards beneath the arch of aorta to the hilum of the left lung.
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Relations— Anterior. —The left pulmonary artery, which sut quently lies above it. Posterior. —The oesophagus and the descend thoracic aorta.
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The left bronchus has no eparterial branch.
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When the interior of the trachea is viewed from above, as in usii the laryngoscope, the openings of the two bronchi are seen to 1 separated by a ridge which is situated to the left of the median lin and more of the interior of the right bronchus than of the left is visibl Partly on this account, and partly by reason of the more vertic
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THE THORAX
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1087
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tion of the right bronchus, as well as its larger size, a foreign - getting into the trachea is more apt to descend into the right chus than into the left.
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'he structure of the trachea will be described in connection with description of the windpipe in the neck.
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Esophagus in the Thorax. —The oesophagus or gullet extends from pharynx to the stomach. In the first part of its course it lies ie neck, and this portion will be found described in connection with region. The thoracic part (see Fig. 651) extends from the level he upper border of the manubrium sterni to the level of the / of the eleventh thoracic vertebra, where, ng previously passed through the oesophaopening of the .diaphragm, it terminates
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he cardiac orifice of the stomach. Its
 +
se is not quite vertical. At its commencet the thoracic portion lies partially to the of the middle line, but as it descends it es to occupy a median position about the 1 of the fifth thoracic vertebra, and in>rly it again inclines partially to the left, ccupies the superior and posterior mediasI spaces, and lies in front of the verte. column, accurately following the thoracic 3ro-posterior curve.
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Relations— Anterior .—The trachea as low
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he intervertebral disc between the bodies
 +
he fourth and fifth thoracic vertebrae; the it pulmonary artery; the root of the left [ichus; the posterior wall of the pericardium nsite the back of the left atrium of the rt; and the vertebral portion of the diaagm. Posterior .—The vertebral column; longus cervicis muscles, especially the left; thoracic duct and vena azygos; the right terior intercostal arteries; the upper and er transverse azygos veins; and interiorly descending aorta. Right .—The right erior and posterior mediastinal pleurae. Left. The thoracic portion the left subclavian artery; the upper part of the thoracic duct, left superior mediastinal pleura above and the left posterior iiastinal pleura just before it pierces the diaphragm, and the cending aorta, except inferiorly.
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The right and left vagus nerves are intimately related to the cesoigus. They are at first disposed laterally, and their branches give i to the oesophageal plexus. Subsequently the right vagus nerve cends on the posterior surface of the oesophagus, and the left on
 +
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anterior surface, in which positions they accompany the gul et
 +
ough the oesophageal opening of the diaphragm.
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Fig. 648.—To show Relations between Aorta, Trachea and (Esophagus (from the Front).
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io88
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A MANUAL OF ANATOMY
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Blood-supply—Arteries. —These are (i) the oesophageal brai of the descending aorta, (2) the oesophageal branches of the left gc artery, and (3) twigs from the left phrenic artery. In the necl oesophagus receives branches from the right and left inferior tin arteries.
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 +
The veins accompany the corresponding arteries, and term: in the vena azygos and the two venae hemiazygos.
 +
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Lymphatics. — These pass to posterior mediastinal glands whic mainly in front of the oesophagus.
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Nerves. —These are derived fron vagus and sympathetic nerves.
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S
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Structure. —The wall of the oesopl consists of three coats—namely, muse submucous, and mucous.
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The muscular coat is thick, and is posed in two layers, an external longitu and an internal circular.
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The longitudinal muscular fibres ar< tached superiorly to the upper part o: median ridge on the posterior surface o cricoid cartilage, and from this point descend as two flattened bands, one on e side of the tube. These expand and meet, giving rise to one continuous 1 which completely surrounds the oesophe Interiorly they are continuous with longitudinal muscular fibres of the stoir Accessory fleshy slips are described as pai from this layer to the back of the trac the back of the root of the left bronc the pericardium, and the left pleura.
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The circular muscular fibres are con ous superiorly with the lower fibres of
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Fig. 649.— Diagram to show _ __ a __ j _
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Pleural Relations (Thick inferior constrictor muscles of the pha: Black Lines) of (Esophagus and interiorly with the circular, and (Frontal Section). with the oblique, muscular fibres of
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stomach.
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The muscular tissue of the oesophagus is of the striated variety over abou upper third of the tube, but elsewhere it is of the plain or non-striated vai
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The submucous coat consists of loose areolar tissue, which contains larger bloodvessels and the mucous glands.
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The mucous membrane is thick, and is thrown into longitudinal fold account of the loose disposition of the submucous coat. The portion of it the submucous coat consists of plain muscular fibres, which are arranged 1 tudinally. This portion is known as the muscidaris mucosce, and it is marked in the lower part of the oesophagus. The inner surface of the mi coat is provided with numerous papillae, and it is covered by stratified squai epithelium, which is thrown into elevations by the papillae.
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The mucous glands are racemose, and are situated in the submucous 1 Their ducts are large and long, and on their way to the free surface son them traverse small collections of lymphoid tissue.
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Development. —The oesophagus is developed from that part of the for( which succeeds to the portion from which the pharynx is developed. At fh is very short, on account of the imperfect development of the neck. As, howi
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THE THORAX
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1089
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leek becomes formed, and as the stomach descends, the oesophagus becomes rated.
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descending Aorta. —The descending aorta, which is the continuaof the aortic arch, commences on the left side of the body of fourth thoracic vertebra on a level with its lower border, and linates at the lower border of the body of the twelfth thoracic ebra. At the latter level it* passes through the aortic opening lie diaphragm, and enters upon the abdominal part of its course, vessel lies in the posterior mediastinum, and its course is down
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Stratified Epithelium Mucous Membrane Muscularis Mucosae
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Submucosa
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ircular Muscular Fibres
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Longitudinal Muscular Fibres
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- Mucous Gland
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Fibrous Sheath
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Fig. 650.—Transverse Section of the Wall of the (Esophagus.
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is and medially, so that, though at first on the left side of the vertecolumn, it subsequently takes up a position in front of it. Relations — Anterior .—From above downwards, the root of the lung; the pericardium; the oesophagus; and the vertebral portion
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he diaphragm. Posterior .—The bodies and intervertebral discs
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tioracic vertebrae below the fourth; and the upper and lower transie azygos veins. Right .—The oesophagus superiorly; the thoracic t; and the vena azygos. Left .—The left superior and posterior Liastinal pleurae; and the upper and lower left azygos veins. In}dy the oesophagus inclines slightly to the left. It is to be noted
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logo
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A MANUAL OF ANATOMY
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that the oesophagus has a threefold relation to the descending ac At first it lies upon the right side of the vessel; then directly in f: of it; and finally it inclines slightly to its left side.
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Branches. —These are as follows: bronchial, pericardial, cesopha^ mediastinal, posterior intercostal and subcostal.
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Trachea
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Left Common Carotid Artery Scalenus Anterior Muscle
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Innominate
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Artery
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Left Vagus Nerve
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Rt. Superior Intercostal Artery
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_ Left Subclavian Artery (Third Part)
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Lefi Phrenic Nerve
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Arch of.., Aorta
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Left Superior Intercostal Artery
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Cardiac Branches of Cer Sympathetic Ganglia Vagus
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- Superficial Cardiac Plexi
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Left Bronchus
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. Descending Thoracic Aorta
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(Esophagus
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Posterior Intercostal Vesiels and Nerve
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- Abdominal Aorta
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Fig. 651 —Dissection of the Posterior Wall of the Thorax.
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The bronchial arteries supply the lungs and the bronchial lymph glands. They are usually three in number—one right and two 1 The right bronchial artery arises from the aorta in common with upper left bronchial artery, or sometimes from the first right poste intercostal artery. The two left bronchial arteries, upper and lo\
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THE THORAX
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1091
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directly from the aorta near each other. The arteries enter the
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ective lungs behind the bronchi, and in their further course and -ibution they follow the ramifications of he bronchial tubes, fhe bronchial veins accompany the corre ponding arteries. The
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vein opens into the vena azygos; and the left vein opens either
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the superior vena hemiazygos or into the left superior interal vein. The bronchial veins are conrably smaller than the corresponding ries.
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rhe pericardial branches supply the pos >r part of the pericardium, rhe oesophageal branches are numerous, arise at irregular intervals. Superiorly 7 spring from the right side of the aorta, inferiorly from its anterior wall. They stomose freely with one another along wall of the oesophagus: superiorly with oesophageal branches of the inferior
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oid arteries, and inferiorly with the
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phageal branches of the left gastric ry, the latter branches entering the ■ax through the oesophageal opening of diaphragm.
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The mediastinal branches are very minute, supply the lymphatic glands and areolar le in the posterior mediastinum.
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The posterior intercostal arteries are ar^ed in pairs, and are nine in number on 1 side. They are destined for the lower 5 intercostal spaces, the first two spaces lg supplied by the superior intercostal
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ry, which is a branch of the second part
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he subclavian on the right side, and of
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first part on the left side. They arise in
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s from the posterior wall of the descendaorta, and pass outwards upon the bodies
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he vertebrae to the posterior extremities
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he intercostal spaces. The arteries of
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right side pass behind the oesophagus, thoracic duct, and the vena azygos; l those of the left side pass behind the erior and inferior venae hemiazygos acding to their level. The arteries of both sides pass behind the ipathetic trunk. The upper right posterior intercostal arteries longer than those of the left side, on account of the position of the cending aorta on the left side of the vertebral column. All the sries lie behind the parietal pleura. Each artery, on entering an ircostal space, lies at first between the parietal pleura and the
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Fig. 652.—To show the Relations to Each Other of the Aorta, Thoracic Duct, Azygos Vein, and Intercostal Arteries (Anterior View).
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1092
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A MANUAL OF ANATOMY
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posterior intercostal membrane. Its course is outwards and slig] upwards, and partly on this latter account, but chiefly on acco of the downward slope of the rib, it soon gains the lower borde: the upper rib. At a point corresponding to the angle of the rib
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artery pierces the posterior intercostal membrane, and passing betw< the external and internal intercostal muscles, it enters the costal gro( of the upper rib. In this position it courses forwards, and ends anastomosing with the upper anterior intercostal branch of the inter
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THE THORAX
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1093
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unary artery, or of its musculo-phrenic branch, according to the
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he companion intercostal vein lies above the artery, and the
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sponding intercostal nerve lies below it. The order of structherefore, in the costal groove, from above downwards, is as
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ws: intercostal vein, intercostal artery, and intercostal nerve, upper seven posterior intercostal arteries are confined to the costal spaces which they occupy; but the lower two—namely, 3 in the tenth and eleventh intercostal spaces—ultimately leave i spaces, and pass into the abdominal wall, where they have been
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ibed in connection with the abdomen.
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•ranches. —These are posterior, giving off a spinal branch; collateral costal; and lateral cutaneous.
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he posterior branch arises from the posterior intercostal artery as vessel enters the posterior extremity of an intercostal space. It is backwards, in company with the posterior primary division of the isponding spinal nerve, between the adjacent transverse processes, ■e it lies internal to the superior costo-transverse ligament. Ope the intervertebral foramen it gives off its spinal branch , which
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s the vertebral canal through the foramen to be distributed to
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sseous and ligamentous walls, as well as to the spinal cord and its branes. The posterior branch, continuing its course backwards, les into a medial and lateral branch, which supply the muscles integument of the back.
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he collateral intercostal artery arises from the main posterior interil opposite the angle of the rib. It passes obliquely downwards outwards to the upper border of the lower rib, along which it >es, lying between the external and internal intercostal muscles, riorly it ends by anastomosing with the lower anterior intercostal
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h of the internal mammary artery, or of its musculo-phrenic
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"h, according to the level.
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he lateral cutaneous branches accompany the lateral cutaneous dies of the corresponding intercostal nerves to the integument, he first posterior intercostal artery—namely, that which lies in bird intercostal space—furnishes a branch, of variable size, which ids over the neck of the third rib to the second intercostal space, branch anastomoses with the second posterior intercostal artery, h is a branch of the superior intercostal, and may even replace it. he subcostal arteries , right and left, are the last branches of the ending thoracic aorta. They are serially continuous with the rior intercostal arteries above, and with the lumbar arteries below, vessel winds round the side of the body of the twelfth thoracic bra, and, passing beneath the lateral arcuate ligament of the iragm, enters the wall of the abdomen, where it lies along the lower t of the twelfth rib. These vessels will be found described in action with the abdomen (see p. 848).
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he first and second intercostal spaces receive their arteries from uperior intercostal artery, which is a branch of the second part
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1094
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A MANUAL OF ANATOMY
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of the subclavian on the right side, and of the first part on the side. Having descended in front of the neck of the first rib to posterior extremity of the first intercostal space, the vessel furni the first posterior intercostal artery to that space, and it also g off the second posterior intercostal artery, which descends in f of the neck of the second rib to the second intercostal space, stated, the second posterior intercostal artery receives a branch f the third posterior intercostal artery, which ascends over the : of the third rib.
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Development of the Descending Aorta. —The upper portion of the descei
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aorta is developed from that part of the left primitive dorsal aorta whicl between the fourth left aortic arch and the place of junction of the two prin dorsal aortae. The greater portion of it, however, results from the union c two primitive dorsal aortae. The posterior intercostal arteries are deve^ from thoracic intersegmental arteries.
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Posterior Intercostal Veins. —The intercostal veins are eleve: number on either side, and each lies in the costal groove above corresponding posterior intercostal artery. In the region of the a of the rib each vein receives the collateral intercostal vein, which acc panies the artery of that name. At the posterior extremity o intercostal space each vein receives a large posterior branch, w returns blood from the muscles and integument of the back, external vertebral venous plexus, and the vertebral canal. Witt exception of the upper three or four veins, all the other intero veins pass inwards, behind the corresponding sympathetic cord to the bodies of the thoracic vertebrae, from which they receive s twigs. Their mode of termination differs on the two sides. On right side the veins, having passed behind the oesophagus, termi in the vena azygos. On the left side the lower four veins—namely eighth, ninth, tenth, and eleventh—open into the inferior vena h azygos; and the succeeding three (or four)—namely, the fifth, s: and seventh (and, it may be, the fourth also)—open into the sup vena hemiazygos.
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The first posterior intercostal vein of each side accompanies corresponding superior intercostal artery, and terminates in innominate vein, or, it may be, in the vertebral vein, of its own si(
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The second and third posterior intercostal veins (and, it may be fourth) of each side unite to form the superior intercostal vein, right superior intercostal vein, after a downward course, joins the u part of the vena azygos. The left superior intercostal vein fori loop which lies in front of the arch of the aorta, and opens intc left innominate vein. It sometimes receives the left bronchial as a tributary.
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Summary of the Posterior Intercostal Veins—Right Posterior Inter Veins. —The first opens into the right innominate vein, or sometimes into the vertebra] vein. The second and third (and, it may be, the fourth also) to form the right superior intercostal vein, which opens into the vena a2 The lower eight (sometimes the lower seven) are direct tributaries of the ' azygos.
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THE THORAX
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1095
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Left Posterior Intercostal Veins. —The first opens into the left innominate n, or sometimes into the left vertebral vein. The second and third (and, it ,y be, the fourth also) unite to form the left superior intercostal vein, which 3ns into the left innominate vein. The fifth, sixth, and seventh (and, it may the fourth also) terminate in the superior vena hemiazygos. The eighth, ith, tenth, and eleventh are tributaries of the inferior vena hemiazygos.
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The left superior intercostal vein is developed from two sources. The upper vt is formed by the portion of the left anterior cardinal vein below, and jacent to, the commencement of the transverse jugular vein. The lower part 'ormed by the upper portion of the left cardinal vein.
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Intercostal Glands. —These glands form a chain on either side of the vertebral umn, in line with the necks of the ribs. The main glands of each chain lie
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g. 654.— Vena Azygos and Right Sympathetic Chain, showing Ganglia and the Greater and Lesser Splanchnic Nerves arising from it.
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Ph. N, phrenic nerve.
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the posterior parts of the intercostal spaces, and one or two glands accompany ch posterior intercostal artery for a very short distance.
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The intercostal glands receive their afferent vessels from (1) the posterior half the costal pleura, (2) the posterior halves of the external and internal interstal muscles, (3) the deep muscles of the back, and (4) the vertebral canal, leir efferent vessels, on either side, pass to the thoracic duct; those from the >ver four or five spaces usually unite to form a trunk which, running vertically wnwards, pierces the diaphragm, and opens into the thoracic duct near its mmencement, or it may be into the cisterna chyli itself.
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The efferents of the upper right intercostal glands sometimes open into a >ht broncho-mediastinal lymphatic trunk, which terminates in the right tnphatic duct.
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The right superior intercostal vein is developed from the anastomotic channels iiich connect the upper three thoracic segmental veins of the right side. •
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A MANUAL OF ANATOMY
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1096
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The Venae Azygos et Hemiazygos Veins.—The vena azygos (ve azygos major) commences in the abdomen as the right ascendi lumbar vein , and enters the thorax through the aortic opening of t diaphragm, lying on the right side of the aorta, the thoracic dr intervening. It then ascends, under cover of the oesophagus, up
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Right Lymphatic Duct
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Right Innominate Vein
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Superior Vena Cava.Right Superior Intercostal Vein.
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Vena Azygos —\
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Thoracic Duct—A
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Posterior Intercostal Glands
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Cistema Chyli Right Ascending Lumbar Vein..
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Inferior Vena Cava__.
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Thoracic Duct
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S 3 Left Innominate Vein
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IT'
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- Left Superior Intercostal Vein L. Arch of Aorta
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- Superior Vena Hemiazygos
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Upper Transverse Azygos Vein
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— Lower Transverse Azygos Vein
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— Ninth Posterior Intercostal Vein
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- Inferior Vena Hemiazygos
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-.Left Subcostal Vein
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__Quadratus Lumborum —Left Ascending Lumbar Vein
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--Abdominal Aorta
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— Iliac Crest -Psoas Major
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—.Uiacus
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.'xCommon Iliac Arteries
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Fig. 655.—The. Thoracic Duct, Azygos and Hemiazygos Veins, and
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Posterior Intercostal Glands.
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the bodies of the thoracic vertebrae, crossing in its course the rig posterior intercostal arteries. Having reached the level of the fif thoracic vertebra it leaves the vertebral column, and arching forwar over the right bronchus it opens into the superior vena cava ju! before that vessel pierces the pericardium. In the thorax the vei
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THE THORAX
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1097
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is continues to lie on the right side of the aorta, the thoracic duct /ening.
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ributaries. —These are as follows:
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The right subcostal vein.
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The lower seven (sometimes the lower eight) right posterior
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ostal veins.
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The right superior intercostal vein.
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The right bronchial vein.
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Some oesophageal veins.
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Some pericardial veins.
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The lower and upper transverse azygos veins, he inferior vena hemiazygos (vena azygos minor inferior) commences 3 abdomen as the left ascending lumbar vein, and enters the thorax iercing the left crus of the diaphragm. It ascends upon the bral column to the level of the eighth thoracic vertebra, lying in of the lower posterior intercostal arteries, and it takes up the • four left posterior intercostal veins. It then crosses the vertebral in from left to right under the name of the lower transverse azygos passing behind the descending aorta and thoracic duct, and ing into the vena azygos, ributaries. —These are as follows:
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1. The left subcostal vein.
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2. The lower four left posterior intercostal veins.
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3. Some oesophageal veins.
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he superior vena hemiazygos (vena azygos minor inferior) is formed le union of the fifth, sixth, and seventh left posterior intercostal
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(sometimes also the fourth). At the level of the seventh thoracic
 +
bra it crosses the vertebral column from left to right under the 5 of the upper transverse azygos vein, passing behind the descending 1 and thoracic duct, and opening into the vena azygos. It comicates above with the left superior intercostal vein, and below the inferior vena hemiazygos, ributaries. —These are as follows:
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. The fifth, sixth, and seventh left posterior intercostal veins etimes also the fourth).
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. The left bronchial vein, as a rule.
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. Some oesophageal veins.
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he superior and inferior venae hemiazygos, which are subject to 1 variation, sometimes unite to form one transverse azygos vein, he other hand, the hemiazygos veins are not infrequently multiple, multiple openings into the vena azygos.
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unmary of the Azygos and Hemiazygos Veins—Vena Azygos. This vessel /es (1) the right subcostal vein; (2) the lower seven (sometimes the lower ) right posterior intercostal veins; (3) the right superior intercostal vein;
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right bronchial vein; (5) some oesophageal veins; (6) some pericardial
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and (7) the lower and upper transverse azygos veins,
 +
iferior Vena Hemiazygos. —This vessel receives (1) the left subcostal vein; lower four left posterior intercostal veins; and (3) some oesophageal veins.
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A MANUAL OF ANATOMY
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1098
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Superior Vena Hemiazygos. —This vessel receives (1) the fifth, sixth, seventh (sometimes also the fourth) left posterior intercostal veins; (2) tb bronchial vein, as a rule; and (3) some oesophageal veins.
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The vena azygos and the inferior vena hemiazygos, through connection with the ascending lumbar veins, establish communica with the inferior vena cava and with the common iliac veins or < of their tributaries. They therefore form important channels by wh considerable quantity of blood is returned from the lower limbs abdominal wall in cases of obstruction of the inferior vena cava, vense azygos et hemiazygos frequently communicate with the renal v
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Fig. 656.—To show the Derivation of the Azygos Veins.
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First figure shows original symmetry, the primitive jugular (PJ) on each joining the cardinal (C) to make the duct of Cuvier (D), which enter sinus venosus (SV); the duct of Cuvier is intrapericardial. In the se figure the left innominate vein (LIV) is formed, taking over the left ju and subclavian drainage, and leading to the appearance of a f superior cava.’ Further changes on left side affect the cardinal, which is rec in size and broken in various ways, such as in the next figure. The ' sup intercostal vein ’ here is seen to be formed from cardinal (C) and terr piece of jugular (PJ), and at the junction of these parts the duct of G (D) is present as an obliterated remnant; the lower left intercostals ( to the right vein by two cross-connections. The longitudinal left vein persist, with connections, or (as in figures) the lower left veins may separately, or may join to form one large transverse vessel, or some n fication of these variations may be found.
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Development. —The azygos vein is developed at its upper end from terminal part of the right cardinal vein; below the mid-thoracic level it is r by supracardinal (periganglionic) reaching the cardinal through an interme* piece of subcardinal. The hemiazygos veins (lower) are derived from the supracardinal, developing transverse retro-aortic connections. The V hemiazygos (left superior intercostal) is partly cardinal and (at its termina primitive jugular (see Fig. 656).
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Subcostal Veins .—These are two in number, right and left, they are serially continuous with the intercostal veins. Each v( enters the thorax from the abdomen by passing behind the lat
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THE THORAX
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1099
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late ligament of the diaphragm. As stated, the right vein opens 1 the vena azygos, and the left into the inferior vena hemiazygos.
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Anterior Primary Rami of the Thoracic Spinal Nerves.— These are Ive in number on each side. The first eleven enter intercostal
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aces, and are called the intercostal nerves. The last, which belongs the abdomen, lies along the lower border of the twelfth rib, and is Ued the subcostal nerve (‘ last dorsal nerve ). At the posterioi tremities of the intercostal spaces the intercostal nerves are near
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 +
IIOO
 +
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A MANUAL OF ANATOMY
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the sympathetic trunk, and each nerve is connected with the adjace sympathetic ganglion by two rami communicantes, which are nee! sarily very short. One of these rami, being composed of spinal fibr is white, and the other, which consists of sympathetic fibres, is gr\ Each intercostal nerve lies below the corresponding artery, and, li it, lies between the parietal pleura and the posterior intercos membrane as far as the angle of the rib. Its subsequent course cor:sponds to that of the artery. The first intercostal nerve is of sm; size, because the greater part of the anterior primary ramus of tj first thoracic nerve takes part in the formation of the brachial plexij The second intercostal nerve sometimes gives off a small bran^ which ascends to join the portion of the anterior primary ramus the first thoracic nerve which takes part in the brachial plexus. Tj further course and distribution of the intercostal nerves belong to tl thoracic and abdominal walls, in connection with which they willfound described.
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Thoracic Duct. —The thoracic duct commences in the abdony in a dilatation, called the cisterna chyli (receptaculum chyli), which situated in front of the bodies of the first and second lumbar vertehi! and terminates by opening into the angle of junction of the interij jugular and subclavian veins of the left side. It is about 18 inci in length, and enters the thorax from the abdomen by passing throu the aortic opening of the diaphragm, where it lies between the aoil on the left and the vena azygos. In this position it ascends in t thorax, resting upon the vertebral column, the right posterior inti costal arteries, and the lower and upper transverse azygos veil being under cover of the oesophagus. Up to the level of the four, or fifth thoracic vertebra it occupies the middle line. At this level passes behind the arch of the aorta, inclining to the left of the mid( line. It then ascends in close contact with the left side of the oesophagi and behind the thoracic portion of the left subclavian artery. In t] position it enters the root of the neck on the left side, where it ascen upon the left side of the oesophagus between the left common carol and left subclavian arteries. At about the level of the seven cervical vertebra it describes a curve, and passes outwards, forwarc and downwards in contact with the dome of the left pleura. It ne inclines inwards, and terminates by opening into the angle of junctk between the internal jugular and subclavian veins of the left sic In the lower part of the thorax the thoracic duct is of smaller calit than in the upper part. Its course is somewhat undulating, ar when distended it presents a beaded appearance, especially in t upper part, due to the number of valves with which it is provide Sometimes the duct divides into two branches in the lower part the thorax, which reunite at a higher level. The duct is freely provid with valves, especially in its upper part, and at its termination there’ an important valve, consisting of two segments, which are so direct as to prevent effectually the reflux of chyle, or the flow of blood in the duct.
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THE THORAX
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IIOI
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he thoracic duct receives lymphatic vessels from the following es: (i) the lower limbs; (2) the abdomen and its viscera, except of the lymphatics from part of the upper surface of the liver; le left half of the thoracic wall; (4) the left lung and the left half e heart; (5) the lower right intercostal spaces; (6) the left upper
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and (7) the left side of the head and neck. Most of the lymphatics
 +
e right half of the thorax and those of the right lung and right of the heart pass to the right lymphatic duct, for the description lich see the section dealing with the neck.
 +
 +
horacic Lymphatic Glands. —These are arranged in several groups ollows: internal mammary; intercostal; innominate; anterior astinal; posterior mediastinal; tracheo-bronchial, and caval. he internal mammary lymph glands (sternal lymph glands) will iund described on p. 996. They receive their afferent vessels from tie anterior parts of the upper six intercostal spaces; (2) the inner on of the mammary gland; (3) the lymphatics accompanying the rior epigastric artery from the upper part of the anterior abdominal
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(4) the lymphatics accompanying the musculo-phrenic artery
 +
the anterior parts of the seventh, eighth, and ninth intercostal es, and from a portion of the diaphragm; and (5) the lymphatics . the anterior set of diaphragmatic glands. The efferent vessels le right glands terminate in the right lymphatic duct, and those
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Le left glands in the thoracic duct. .
 +
 +
die intercostal lymph glands are situated on either side of the sbral column, where they lie in the intercostal spaces, there being l one to three in each space. They receive their afferent vessels l (1) the posterior parts of the intercostal spaces; (2) the parietal ra; (3) the vertebral canal; and (4) the deep muscles of the back, efferent vessels of the left intercostal glands open into the thoracic
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. On the right side the efferent vessels from the lower glands
 +
to the thoracic duct, but those from the upper glands open into
 +
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right lymphatic duct. ..11
 +
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rhe innominate lymph glands (superior mediastinal lymph glands)
 +
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n the superior mediastinum in relation to the arch of the aorta the innominate veins; they are continuous with the posterior iastinal and tracheo-bronchial glands below and with the chain >unph glands along the recurrent laryngeal nerves above. Ihey ive their afferent vessels from the pericardium, the heart, trachea, phagus, and the thymus in early life, and their efferent vesse s
 +
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to the thoracic duct and right lymphatic duct. .
 +
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fhe innominate lymph glands (anterior mediastinal lymph glands)
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a the lower part of the anterior mediastinum in front of the penium. They receive their afferent vessels from (1) the median portions tie right and left lobes of the liver in the vicinity of the lalci orm nent; (2) the adjacent portion of the diaphragm; (3) the anterior of the pericardium. Their efferent vessels pass to the interna
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unary lymph glands. . . , .
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the posterior mediastinal lymph glands are situated m the posterior
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1102
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A MANUAL OF ANATOMY
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Auriculo temporal Nerve Facial Nerve
 +
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Posterior Auricular Nerve >,
 +
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Glosso-pharyngeal Nerve Accessory Nerve
 +
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Hypoglossal Nerve
 +
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] Superior Laryngeal Nerve Vagus Nerve
 +
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Middle Cervical Sympathetic Ganglion
 +
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Recurrent Laryngeal Nerve Cardiac Branches of Vagus
 +
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Ri >ht Posterior Pulmonary Plexus
 +
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Vena Azygos Vascular Branch
 +
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Intercostal Vessels f and Nerve l
 +
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Ramus Communicans
 +
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Sympathetic Trunk
 +
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Abdominal Aorta
 +
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Right Ansa Subclavia
 +
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First Thoracic Ganglion
 +
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Phrenic Nerve
 +
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Root of Right Lui
 +
 +
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. Right Vagus N< on (Esophagi
 +
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(Esophageal I J le:
 +
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Liver (cut)
 +
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Left Vagus Ner
 +
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Descending Aor Thoracic Duct
 +
 +
 +
Lesser Splanchic Nerve Greater Splanchnic Nerve •
 +
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Lowest Splanchic Nerve
 +
 +
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| Branches of V / on Stomac
 +
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Right Coeliac Gangl
 +
 +
— Coeliac Plexus
 +
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Superior Mesenteric Arl and Plexus
 +
 +
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Greater Occipital Nerve
 +
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Hypoglossal Nerve
 +
 +
 +
Sup. Cervical Symp. Ganglion External Carotid Artery Internal Carotid Artery
 +
 +
Sympathetic Trunk
 +
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Com. Car. Art. and Symp. Plexus Phrenic Nerve
 +
 +
 +
Renal Artery and Plexus
 +
 +
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S.V.C. Superior Vena Cava
 +
 +
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Fig. 658.—Nerves of the Right Side of the Face, Neck, and Thor/
 +
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(Hirschfeld and Leveille). * I
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THE THORAX
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1103
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iastinum, along the course of the descending aorta and oesophagus. j receive their afferent vessels from the oesophagus, the posterior of the pericardium, and the vertebral portion of the diaphragm, r efferent vessels pass, for the most part, to the thoracic duct.
 +
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, 659.—A Dissection of the Right Apical Region to show the Stellate Ganglion (viewed from below after removal of the Pleura).
 +
 +
iddition to the subclavian vessels, the lower two brachial nerves are seen, with the ganglion and the superior intercostal artery.
 +
 +
The tracheo-bronchial lymph glands are very numerous, and are iated partly in the angle between the trachea and bronchi, partly ween the two bronchi, and partly at the root of each lung. They very dark in colour, and receive their afferent vessels from the lungs 1 the visceral pleurse. Their efferent vessels pass to the thoracic 't and right lymphatic duct.
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t
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iio4
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A MANUAL OF ANATOMY
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n.c.
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n,C
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The caval glands are situated in contact with the limited tho: portion of the inferior vena cava. They receive their afferent ve from the bare area of the posterior surface of the liver, and also t deep lymphatics of that organ which accompany the hepatic veir the fossa for inferior vena cava. Their efferent vessels pass to
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thoracic duct. One of these glands often be found lying upon the inf< vena cava within the fibrous pericardi The Thoracic Part of the Sympatl System. —The sympathetic system in thorax consists of (i) two gangli: trunks, right and left; and (2) a vertebral plexus — namely, the car plexus. The latter plexus has 1 already described. The gangliated tr lies on each side of the vertebral coll behind the parietal pleura, and superf to the posterior intercostal vessels, presents, as a rule, eleven ganglia, first or stellate ganglion is situated at inner end of the first intercostal sp and probably is formed by the fusioi two originally distinct ganglia; the sec ganglion lies on the head of the third and the other ganglia follow in more less regular sequence, lying on the he of the ribs until the last two ganglia reached; these lie upon the sides of bodies of the eleventh and twelfth thor; vertebrae. The first thoracic ganglioi the largest of the thoracic series, and 1 previously known as stellate ganglion. sympathetic trunk leaves the thorax Fig. 660. — Scheme of the passing behind the inner part of
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R.C.
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R C,
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s.s
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Thoracic Part of the me dial arcuate ligament of the diaphra Flower) an d so enters the abdomen.
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r to 12. Thoracic Ganglia
 +
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R. C. Rami Communicantes
 +
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B.D. Branches of Distribution from Upper Ganglia
 +
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G.S. Greater Splanchic Nerve and Ganglion
 +
 +
S. S. Lesser Splanchnic Nerve L. S. Lowes t Splanchnic Nerve
 +
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Branches — 1. Of Communicatioi
 +
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These are called the rami communicant Two of these, one white and the 0 grey, pass between each ganglion and adjacent intercostal nerve. The w fibres are of spinal and the grey of s pathetic origin. From the proximity of the ganglia to the intercc nerves the rami communicantes are necessarily short.
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2. Of Distribution. —From the upper five ganglia small vase branches are given off, which are distributed to the coats of the thor; aorta. From the second, third, and fourth ganglia pulmor branches are given off to the posterior pulmonary plexus. From
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THE THORAX
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1105
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^anglion downwards the three splanchnic (‘ visceral ’) nerves— »r, lesser, and lowest—are given off.
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le greater splanchnic nerve arises by five separate roots from the sixth, seventh, eighth, and ninth ganglia, the fibres of the upper being traceable in the sympathetic trunk as high as the second ion. The roots arch obliquely forwards and downwards upon des of the bodies of the adjacent vertebrae, and by their union form a large nerve, which pierces the crus of the diaphragm and nates in the cceliac ganglion. The greater splanchnic nerve ins a large number of spinal fibres, which impart to it a white r and firm consistence. The right nerve presents a small ganglion before it leaves the thorax, called the splanchnic ganglion , there may be one on the left nerve. The greater splanchnic
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gives vascular branches to the lower part of the thoracic
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>•
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he lesser splanchnic nerve arises by two roots from the ninth and l ganglia. It pierces the crus of the diaphragm, and terminates e aortico-renal ganglion of the coeliac plexus, he lowest splanchnic nerve, which is sometimes absent, arises ne root from the eleventh ganglion. It either passes behind the al arcuate ligament of the diaphragm or through the crus, and it inates in the renal plexus. When the lowest splanchnic nerve sent, its place may be taken by a branch from the lesser splanchnic
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2k
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araganglia. —Situated in close relationship to the sympathetic lia are small bodies to which the name of paraganglia has been 1. They consist of chromaphil tissue like that which forms the ilia of the suprarenal glands, and probably secrete a substance h is excitory to non-striped muscle.
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he diaphragm will be found described in connection with the •men.
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The Joints of the Vertebral Column.
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. Joints of the Bodies of the Vertebrae.— These joints belong to class of secondary cartilaginous joints. Ihe ligaments are as ws: the anterior longitudinal ligament, the posterior longitudinal nent, and the intervertebral discs.
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he anterior longitudinal ligament (anterior common ligament) is a
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e band of white glistening fibres, which extends over the anterior ices of the bodies of the vertebrae and intervertebral discs. It nds from the axis to the first segment of the sacrum, and its fibres lisposed longitudinally. Ihe most superficial fibres extend fiom a n vertebra to the fifth below it; the intermediate fibres pass from ven vertebra to the third below it; and the deepest hbies pass 1 a given vertebra to the one immediately below it. The fibres are ly attached to the intervertebral discs and margins of the vertebial ies, but very loosely to the centres of the bodies, on account of the
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70
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iio6
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A MANUAL OF ANATOMY
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presence of bloodvessels. The anterior longitudinal ligamen broadest in the lumbar region, and thickest in the thoracic region, is thicker opposite the centres of the bodies than elsewhere, an these situations it fills up the concavities, and so renders the fror the column less undulating than it otherwise would be. Over lateral surfaces of the bodies a few scattered fibres are present, w pass from one vertebra to that below. In the sacral region the ant< longitudinal ligament is lost in the periosteum of the bone, br reappears lower down as the anterior sacro-coccygeal ligament, anterior longitudinal ligament is serially continuous superiorly with anterior atlanto-occipital membrane.
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Posterior Band of Superior Costo-transverse Ligament
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Anterior Band of Superior Costo-transverse Ligament
 +
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Three Slips of i Radiate Ligament p
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Intra-articular Ligament"
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- Anterior Longitudinal Ligament
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-■-Hi— Intervertebral Disc
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Fig. 66i.—Ligaments of the Bodies of the Vertebrae and Joints of
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Heads of the Ribs on the Right Side.
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The posterior longitudinal ligament (posterior common ligamenl
 +
 +
situated within the spinal canal, and extends over the poste surfaces of the bodies of the vertebrae and intervertebral discs. I broader above than below, and consists of glistening fibres, wl extend from the axis to the first coccygeal vertebra, its sacral p however, being very narrow and delicate. Its fibres are firmly attac to the intervertebral discs and margins of the vertebral bodies, but t are separated from the centres of the bodies by the transverse ven communications between the basivertebral veins. In the cerv: region the ligament is of almost uniform breadth, being expanded c the vertebral bodies, as well as over the intervertebral discs. In thoracic and lumbar regions, however, it is narrow opposite vertebral bodies, and broad opposite the intervertebral discs, margins, therefore, present dentations, which give it a denticula
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THE THORAX
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1107
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trance. The arrangement of its fibres is similar to the arrangeof those of the anterior longitudinal ligament. The posterior
 +
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udinal ligament is serially continuous superiorly with the
 +
Drana tectoria.
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be intervertebral discs are situated between the adjacent surfaces e bodies of the vertebrae, and they constitute the chief bond of l between them. Their outline corresponds to that of the bodies sen which they are placed, and they are elastic and compressible, pt in early life, the first or highest disc is situated between the bodies e axis and the third cervical vertebra, and in the adult the last west disc is situated between the bodies of the fifth lumbar and sacral vertebrae.
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l 662. —Posterior Longitudinal Fig. 663. —Intervertebral Discs
 +
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Ligament of the Bodies of the (Anterior View).
 +
 +
Vertebrae.
 +
 +
£ach disc is composed of a circumferential fibrous part, disposed le form of superimposed laminae, and a central portion, the nucleus 1 osus , which is soft and pulpy. The annulus fibrosus forms more 1 half of the disc, and is composed of fibrous tissue and fibroilage. As seen in transverse section the laminae are arranged
 +
 +
entrically around the nucleus pulposus , which they closely embrace
 +
compress. The fibres of which they are composed are arranged >arallel bundles, which extend obliquely between the adjacent ices of the vertebral bodies, being attached to the layer of hyaline ilage which covers them. The fibres of successive laminae pass Tiely in opposite directions, and are disposed thus X. The outer nae consist of fibrous tissue, but the majority are composed of white )-cartilage. As seen in vertical section the outermost laminae are
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no8
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A MANUAL OF ANATOMY
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bent outwards, and those around the nucleus pulposus are bent inw; towards it, this arrangement contributing to the elasticity of the ve bral column. The nucleus pulposus consists of a soft, elastic, pi substance, having a lobate arrangement. Being surrounded compressed on all sides by the annulus fibrosus, when a section i disc is made the nucleus pulposus, being relieved from press projects beyond the level of the cut surface. It is composed ( cellular reticulum, supported by a delicate fibrous stroma.
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The nucleus pulposus is a persistent portion of the notochord.
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The intervertebral discs form about one-fourth of the lengtl the vertebral column, and are thickest in the lumbar region, the cervical and lumbar regions they are deeper in front than beh and they give rise to the curve forwards in the cervical region, wl they increase the forward curve in the lumbar region. In the thor
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region they are of uniform depth. Throughout the column t are intimately connected with the anterior and posterior longitudi ligaments, and, in the thoracic region, with the radiate ligaments ; the intra-articular ligaments of the heads of most of the ribs, the cervical region the discs are not present at either lateral asf of the opposed surfaces of the bodies. In these regions there i synovial space on either side, between the projecting lateral lip of upper surface of the lower body and the bevelled lateral margin of lower surface of the upper body. The opposed surfaces are cove by cartilage, and there is an indistinct capsular ligament.
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2. Ligaments of the Laminae. —These are called the ligame flava (ligamenta subflava). They are strong, thick plates of yel elastic tissue, which connect the laminse together, and they ext from the axis to the first sacral segment. They are best seen from interior of the vertebral canal, and as they extend between the vertel
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THE THORAX
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1109
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2S they close in the canal in these situations. Each ligamentum im extends from the root of the articular process to the place e the lamina joins its fellow to form the spinous process. At point it comes into relation with the ligament of the opposite a small interval being left between the two for the passage of 3. Superiorly the ligament is attached to the anterior surface le upper lamina a little above its lower border, and inferiorly it tached to the upper border, and adjacent part of the posterior ice, of the lower lamina. The ligamenta flava are wider in the ical and lumbar regions than in the thoracic region, and over the ter part of the latter region, as viewed from the exterior, they are ealed from view by the imbricated laminae. Their importance ists in their great elasticity, which enables them to maintain the
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G< 666._Ligamenta Flava in the Lumbar Region (Anterior View).
 +
Ihe pedicles have been sawn through, and the vertebral bodies removed.
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tebral column erect, and to restore it to the erect position after it
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been bent forwards. . . A
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3. Ligaments of the Articular Processes. —Ihe joints between the
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cular processes belong to the class of synovial joints of the le variety. The articular surfaces are covered by cartilage, and joint is surrounded by a capsular ligament s lined with a synovial nbrane. These ligaments are disposed moie looselj 7 in the cervical
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ion than elsewhere. . .
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4. Ligaments of the Spines.— These are supraspinous and mter The supraspinous ligament consists of longitudinal fibres which nect the extremities of the spines. It extends from the spine the seventh cervical vertebra to the spine of the fourth sacral ment, and its fibres are arranged in a manner similar to those of anterior longitudinal ligament. In the cervical region the supralous ligament is replaced by the ligamentum nuchae. ihe interspinous ligaments, which are thin and membranous, are situ between adjacent spines, to the margins of which they are atta( from root to tip. They are strongest in the lumbar region, and in neck they are replaced by deep processes of the ligamentum nucl
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5. The intertransverse ligaments. —These consist of scattered fil which pass between the extremities of the transverse processes in thoracic and lumbar regions. In the neck they are replaced by intertransverse muscles.
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Movements. —The movements allowed in the vertebral column are fle: extension, lateral movement, rotation, and circumduction.
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Flexion and extension are freely allowed in the cervical and lumbar reg: In the thoracic region these movements are very limited on account of (1) small amount of intervertebral substance, and (2) the imbrication of the lam Lateral flexion is allowed in the cervical, thoracic, and lumbar regions, bi the neck it is associated with rotation. During these combined movemeni lateral flexion and rotation in the neck one inferior articular process g upwards and forwards on that which is opposed to it, whilst the other inf< articular process glides downwards and backwards on the one opposed t< Pure rotation is allowed in the thoracic region round an axis corresponding the centre of a circle of which the surfaces of the articular processes form ments. This centre is necessarily anterior to the articular processes, corresponds pretty nearly with the centres of the bodies of the vertebra, the lumbar region rotation is impossible, for the following two reasons: (1) centre of the circle of which the articular processes form segments is poste to these processes; and (2) the articular processes are so disposed as to be loc In the lumbar region circumduction is allowed, which consists in a combina of flexion, extension, and lateral movements.
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Summary of Movements—-Cervical Region. —(1) Flexion and extension;
 +
 +
(2) a combination of lateral flexion and rotation. Thoracic Region. —(1) Fie: and extension, but only to a limited extent; (2) lateral flexion; and (3) ] rotation. Lumbar Region. —(1) Flexion and extension; (2) lateral flexion;
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(3) circumduction.
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 +
The joints of the atlas, axis, and occipital bone will be foi described in the section dealing with the head and neck.
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The Joints of the Ribs, Costal Cartilages, and Sternum.
 +
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1. Ribs—Costo-vertebral Joints. —These are divided into joints
 +
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the heads of the ribs and costo-transverse joints.
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The Joints of the Heads of the Ribs. —These unite the heads of ribs to the bodies of the thoracic vertebrae, and they are sometii spoken of as the capitular joints. They belong to the class of syno 1 joints of the plane variety. The articular surfaces are the facets the heads of the ribs and the costal facets on the sides of the hoc of the thoracic vertebrae—that is to say, the lower facet of the verte above and the upper facet of the vertebra below, the intervertet disc intervening between the two. In the case of the first, the ter the eleventh, and the twelfth vertebrae there is only one facet, and corresponding intervertebral discs do not enter into the joints, uni in the case of the first joint, into which the disc between the sevei cervical and first thoracic vertebrae may enter.
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aments.—These are as follows
 +
radiate, capsular, and intra
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lar.
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e radiate ligament (anterior costo-central ligament) or stellate
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jnt consists of strong white fibres which are attached to the or margin of the head of the rib. From this point the fibres e inwards in three bands, one of which passes upwards to be Led to the body of the vertebra above, a second horizontally is to be attached to the intervertebral disc, and a third vards to be attached to the body of the vertebra below, e case of the first, tenth, eleventh, and twelfth joints, into }f which only one vertebra enters, the ligament is composed of ands, instead of three. In the first joint the lower band passes
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body of the first thoracic vertebra, and the upper band to the
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jsterior Band of Superior 'osto-transverse Ligament
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Vnterior Band of Superior -osto-transverse Ligament
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• Anterior Longitudinal Ligament
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- Intervertebral Disc
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Radiate Ligament —
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>7.—Ligaments of the Bodies of the Vertebra and Joints of the Heads of the Ribs on the Right Side.
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of the seventh cervical. In each of the tenth, eleventh, and th joints the lower band passes to the body with which the head e rib articulates, and the upper band to the body of the vertebra
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e.
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he capsular ligament is incomplete, and consists of thin loose 5, which cover the posterior, superior, and inferior aspects of
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°int. ,
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he intra-articular ligament consists of short stout fibres, which id from the ridge on the head of the rib, separating the two facets, ie intervertebral disc. It divides the joint into two complete vial cavities, and it is wanting in the first, tenth, eleventh, and
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Eth joints. . . .
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here are two distinct synovial membranes in those joints which
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1112
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A MANUAL OF ANATOMY
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are provided with an intra-articular ligament—namely, from second to the ninth inclusive—one being above the ligament and other below it. In those joints in which the intra-articular ligan is absent—namely, the first, tenth, eleventh, and twelfth—ther only one synovial membrane.
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Arterial Supply. —Branches from the posterior intercostal arterie
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Nerve-supply. —Branches from the intercostal nerves.
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Costo-transverse Joints. —These belong to the class of sync joints of the plane variety. The articular surfaces are the facet the tubercle of the rib and the facet on the anterior aspect of extremity of the transverse process of the thoracic vertebra.
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Ligaments. —These are as follows: posterior costo-transve inferior costo-transverse, superior costo-transverse, and capsular.
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The lateral costo-transverse ligament (posterior costo-transv ligament) is a strong flat band, situated on the posterior aspect of joint, and extending from the extremity of the transverse process the non-articular part of the tubercle of the rib. The directior its fibres is outwards.
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The inferior costo-transverse ligament (middle costo-transv
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ligament) consists of short strong fibres which pass between the poste surface of the neck of the rib and the anterior surface of the adjac transverse process—namely, that with which the tubercle of the articulates. Its fibres, which are disposed horizontally, extend fi the joint of the head of the rib to the costo-transverse joint. 1 ligament is rudimentary in the eleventh and twelfth ribs.
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The superior costo-transverse ligament is a broad flat band, lat< in position, the fibres of which pass from the crest on the upper bor of the neck of the rib to the lower border of the transverse pro( immediately above, in the vicinity of its tip. Its fibres are direc upwards and outwards, and its outer border is continuous with posterior intercostal membrane. A feeble band of fibres, medial the preceding, extends from the back of the neck of the rib, below crest, to the lower aspect of the transverse process immediately abc close to its base, being termed the posterior costo-transverse ligamen
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The superior costo-transverse ligament is wanting in the case the first rib.
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The capsular ligament is formed in part by the lateral cos transverse ligament, and elsewhere by a thin loose membrane, fibres of which are attached lateral to the articular processes, is absent in the case of the eleventh and twelfth ribs.
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The synovial membrane is single and small.
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Arterial and Nerve Supply. —Offsets from the posterior branc of the intercostal arteries and nerves.
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The costo-transverse joints are wanting in the case of the eleven and twelfth ribs, and sometimes in the case of the tenth.
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Costo-chondral Joints. —These belong to the class of fibrous joii The outer extremity of the costal cartilage is implanted in the o pit on the anterior extremity of the rib, and the union is effected
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THE THORAX
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1113
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continuity which takes place between the periosteum of the rib the perichondrium of the cartilage.
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2. Costal Cartilages—Sterno-Costal Joints. —These belong to the s of synovial joints, except in the case of the first joint, which mgs to the class of primary cartilaginous joints. The cartilages ch take part in these joints are the first seven on either side,
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e being received into the costal pits or facets on the side of the
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num.
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The ligaments are capsular, sterno-costal, and in the case of the >nd joint at least intra-articular.
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rhe Capsular Ligaments —The anterior part is a triangular band, the er fibres of which ascend upon the sternum, and the lower descend, 1 st the intervening fibres pass horizontally forwards. They de
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Fig. 668. —The Sterno-costal Joints (Anterior View). rhe second, third, and fourth joints of the left side are seen in section.
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sate with those of the opposite side, and blend with the tendinous 'es of origin of the pectoralis major muscle.
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The posterior part of the capsular ligament is disposed in a manner Lilar to the anterior ligament.
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The sterno-costal ligaments pass from the upper and lower borders
 +
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he costal cartilage to the side of the sternum.
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The intra-articular ligament is present in the second joint, and may present in some of those succeeding to it. Its fibres extend horiitally between the centre of the sternal end of the second costal tilage and the plate of fibro-cartilage between the manubrium and ly of the sternum. It divides this joint into two complete synovial dties.
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The first joint has no synovial membrane, the first costal cartilage ng directly united to the manubrium sterni. The second joint, as ted, has two synovial membranes, one above and the other below J intra-articular ligament. The succeeding joints have each usually
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iii4
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A MANUAL OF ANATOMY
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one synovial membrane, but sometimes one or more of them ms have two.
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Arterial Supply. —The perforating branches of the internal mammai artery.
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Nerve-supply. —The intercostal nerves as they are becoming tl anterior cutaneous nerves.
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Interchondral Joints. —These belong to the class of synovial join of the plane variety. The cartilages involved are usually the sixt' seventh, and eighth, but sometimes also the ninth, and it may be tl fifth, and even the tenth. The lower border of each cartilage projec downwards, and comes into contact with the upper border of tl cartilage below. Each joint is surrounded by fibres disposed in tl form of a capsule, and it is provided with a synovial membrane.
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Arterial Supply. —The musculo-phrenic branch of the intern; mammary artery.
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Nerve-supply. —The adjacent intercostal nerves.
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3. Sternal Joints. —The joint between the manubrium and bod of the sternum belongs to the class of secondary cartilaginous joint; The opposed surfaces are covered by hyaline cartilage, and a plat or disc of fibro-cartilage is interposed between them, which is connecte at either side with the intra-articular ligaments of the second sterm costal joint. This disc may contain a small cavity. In front c and behind the joint there are ligamentous fibres which are dispose longitudinally.
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The entire sternum is strengthened by its dense periosteum, b the radiating fibres of the sterno-costal ligaments, and by the tendinor fibres of origin of the pectoralis major muscles.
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Movements of the Ribs. —The movement allowed at the joints of the hear of the ribs and costo-transverse joints is of a gliding nature, and takes place an upward and downward direction. During this movement the rib rotat round the costo-vertebral axis, which corresponds to a line passing obliquej through the joint of the neck of the rib, the neck of the rib, and the costo-tran verse joint. Owing to the curve and downward inclination of the rib, tl result of this rotation is that the anterior and lateral parts of the rib are elevate< Simultaneously, on account of the obliquity of the axis of rotation, the anteric part of the rib is carried forwards, and along with it the sternum, thus increasir the antero-posterior diameter of the thorax. The lateral part of the rib, and to certain extent the anterior part also, are carried outwards, thus giving rise t eversion of the lower border of the rib, and at the same time the angle betwee the rib and its costal cartilage is opened out. In this manner an increase in tl transverse diameter of the thorax is produced. During the elevation of tl anterior and lateral parts of the rib and the eversion of its lower border tl movement takes place round the costo-sternal axis, which corresponds to a lii drawn from the costo-central joint of one side to the corresponding stern< costal joint. It is usual to liken this movement to the movement of the hand of a bucket.
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In the case of the first rib elevation and depression are the chief movemen allowed, the amount of eversion being trivial, inasmuch as the axis of rotatic is almost transverse. In the case of the second, third, fourth, fifth, and six! ribs elevation and depression, along with eversion, are allowed, the axis of rotatio in each case becoming successively more oblique. The seventh, eighth, nintl and tenth ribs, in which the costo-transverse articular surfaces are almost fla'
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THE THORAX
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n 15
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ides rotating round the costo-vertebral axis, also rotate round the costonal axis. In the case of these ribs elevation is accompanied by a backward cement, and depression by a forward movement. These backward and vard movements take place more freely in the case of the eleventh and lfth ribs, which have no costo-transverse joints. At the sterno-costal joints movement is limited, and consists elevation and depression, together ti forward and backward movement.
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At the interchondral joints slight ing movement is allowed.
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Muscles concerned in Respiration.— jrdinary quiet inspiration the muscles cerned are as follows: (1) the diaagm; (2) the external and internal
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rcostal muscles, assuming Haller’s
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v to be correct; (3) the levatores tarum; (4) the serratus posterior suior; (5) the serratus posterior inferior;
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. (6) the quadratus lumborum as being iliarv to the diaphragm, the serratus terior inferior being also auxiliary, inary quiet expiration is due to (1) the
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tic recoil of the lungs, (2) the elastic
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)il of the thoracic wall (costal cartiis and sternum), (3) the sterno-costalis scle, and (4) the muscles of the anteroral wall of the abdomen, which press Ily upon the abdominal viscera, and reby push the diaphragm upwards ards the thorax.
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In forced inspiration the following scles come into play: (1) the scaleni; the sterno-mastoid; (3) the serratus srior ; (4) the pectoralis major and toralis minor; and (5) the latissimus
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si. As auxiliary muscles there are the trapezius, levator scapulae, and rhom1 muscles, which, by their action upon the scapula, fix the shoulder.
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In forced expiration the muscles of the antero-lateral wall of the abdomen with considerable strength, and now depress those ribs with which they connected, and necessarily also the sternum. By some authorities the atus posticus inferior is regarded as being concerned.
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In inspiration the thoracic cavity is enlarged in its vertical, antero-pos terior, transverse diameters. The increase in the vertical diameter is due to the traction and descent of the diaphragm; the increase in the antero-postenor neter is caused by the anterior parts of the ribs, and along with them the num, being carried forwards; and the increase in the transverse diameter rought about by the eversion of the lower borders of the ribs, and the opening of the angles between the ribs and their costal cartilages.
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Fig. 669.— Diagram showing the Axes of Rotation of the Ribs (from Halliburton’s ‘ Handbook of Physiology ').
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A, B, axis passing from the joint of head of rib to chondro-sternal joint; a, b, axis passing through costotransverse and joints of heads of ribs. (The movement round the axis A, B resembles the raising of the handle of a bucket.)

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I have decided to take early retirement in September 2020. During the many years online I have received wonderful feedback from many readers, researchers and students interested in human embryology. I especially thank my research collaborators and contributors to the site. The good news is Embryology will remain online and I will continue my association with UNSW Australia. I look forward to updating and including the many exciting new discoveries in Embryology!

Frazer JE. Buchanan's Manual of Anatomy, including Embryology. (1937) 6th Edition. Bailliere, Tindall And Cox, London.

Buchanan's Manual of Anatomy: I. Terminology and Relative Positions | II. General Embryology | III. Osteology | IV. Bones of Trunk | V. Bones of Head | VI. Bones of Upper Limb | VII. Bones of Lower Limb | VIII. Joints | IX. The Upper Limb | X. Lower Limb | XI. The Abdomen | XII. The Thorax | XIII. Development of Vascular Systems | XIV. The Head and Neck | XV. The Nervous System | XVI. The Eye | XVII. The Ear | Glossary
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Chapter XII The Thorax

Thoracic Wall

Muscles—Intercostal Muscles. — The classic description of t muscles gives them as two in number in each space, external internal, arranged as thin sheets of obliquely-disposed muscular hi with a large admixture of tendinous fibres.

External Intercostal Muscles— Origin .—The lower border of upper rib bounding an intercostal space.

Insertion . — The outer margin of the upper border of the lower

Nerve-supply . — The intercostal nerve of the corresponding spat


Fig. 577. — Diagram of the Intercostal Muscles and Intercostal Artery. A small portion of the external intercostal muscle has been divided and reflected.

The fibres of each muscle are directed downwards and forwc and in this respect coincide with those of the obliquus exte abdominis. The muscles, as a rule, extend as far forwards as junction of the ribs with their cartilages, but sometimes they short of this point, especially in the upper spaces. From the p where the fibres cease the upper six muscles are continued inw to the side of the sternum by a thin delicate membrane, called anterior intercostal membrane. This occupies the spaces between true costal cartilages. Posteriorly the muscles extend as far as tubercles of the ribs.



[nternal Intercostal Muscles. —

Origin. — The upper margin of the al groove of the upper rib.

Insertion. — The inner margin of the upper border of the lower rib. Serve-supply. —The intercostal nerve of the corresponding space, rhe fibres of each muscle are directed downwards and backwards, and lis respect coincide with those of the obliquus internus abdominis, upper six muscles extend as far inwards as the side of the sternum, the lower two are continuous anteriorly with the obliquus internus )minis. Posteriorly the muscles extend as far back as the angles le ribs. In this situation each is replaced by a delicate membrane id the posterior intercostal membrane , which lines the adjacent ion of the external intercostal muscle, and ds behind with the superior costo-transverse nent. The internal intercostal muscles are ired internally by the parietal pleura.

4 ction of the Intercostal Muscles. — This subhas given rise to much discussion and irence of opinion. Three views are entered: (i) According to Haller, the external internal intercostal muscles both act as ators of the ribs, and are therefore muscles ispiration. Inasmuch as the fibres of the muscles decussate, they must, according to view, act on the principle of the parallelon of forces. The common nerve-supply of

Fig. 578. — Diagram of two muscles tends to favour this view. Section across an According to Hamberger, the external inter- ntercostal pace.

al muscles are elevators of the ribs, and El, I, external and in 'efore muscles of inspiration; whilst the inLal intercostal muscles are depressors of ribs, and therefore muscles of expiration.

According to Hutchinson, the external inter:al muscles and the interchondral portions of internal intercostal muscles act as elevators the ribs, and are therefore muscles of ination; whilst the interosseous portions of the internal intercostal scles act as depressors of the ribs, and are therefore muscles of iration.

When a rib is elevated, its lower border is at the same time

rted.


ternal intercostal muscles ; INT, intercost, intimus, or intracostal. Pleura represented by interrupted line. Lateral cutaneous nerve shown between El and I.


Subcostal Muscles. — Deep to the internal intercostal muscles the lains of a third sheet of muscular fibres can often be demonstrated, i sheet is best developed dorsally and in connection with the lower ces. The direction of the fibres is similar to that taken by the cs of the internal intercostal, but unlike these last the fibres, tead of passing between adjacent ribs, pass between ribs some ces apart. The fibres constitute the subcostal muscles, which are the same plane as the sterno-costalis and the costal fibres of the diaphragm, and represent in the thoracic wall the transversus mus of the abdominal wall.

For the levatores costarum muscles, see Index.

It is customary, in modern descriptions of the intercostal muscu ture, to speak of three layers of muscles in this situation. 1 additional fibres are referred to as intercostales intimi: they w described and figured many years ago by Henle, and are usually tal to be partly detached fibres of the internal intercostals. Their fib have the same direction as those of the internal intercostals, from wh they are separated by the intercostal vessels and nerves (Fig. 57 They form a very thin layer, aponeurotic in some places, and tra lucent, better developed in the lower part of the thoracic wall, a more particularly in the middle portions of the spaces.

They are frequently considered to be parts of the same sh as the sterno-costalis (triangularis sterni) and subcostal fibi but this does not seem to be at all certain. If this view is tak the three kinds of muscle are grouped together as the transver thoracis, implying their general continuity with the sheet of abdominal transversus.

Intercostal Nerves.—These are eleven in number on each side, a are the anterior primary divisions of the upper eleven thoracic spi nerves. The anterior primary division of the twelfth thoracic spi nerve is not an intercostal nerve, but lies along the lower border the twelfth rib, and is known as the subcostal nerve (‘ last doi nerve ’).

The lower five intercostal nerves ultimately leave the intercom spaces, and pass into the anterior abdominal wall.

Upper Six Intercostal Nerves .—Each of these nerves, as it ent the back part of an intercostal space, lies between the posterior ini costal membrane and the parietal pleura. About the level of the an of the rib it pierces the posterior intercostal membrane, and pas forwards in the costal groove of the upper rib, lying between intercostal muscles. It continues its forward course in this posit in company with the intercostal artery and intercostal vein, the or of these from above downwards being intercostal vein, intercom artery, and intercostal nerve. The nerve is concealed by the ov lapping lower border of the upper rib.

At (or just beyond) the angles of the ribs between which it is pass the intercostal nerve gives off a collateral branch and, a little furt on, its lateral cutaneous branch. The collateral branch runs forw; along the upper surface of the rib below the space, supplying muscles and terminating either in them or by forming a connect loop with the main nerve some distance from the sternum. The late cutaneous branch pierces the internal intercostal muscle to run forw: between this and the external muscle: it pierces this to reach the surfa the actual site of the perforation varying, of course, according to level of the nerve. The main intercostal nerves themselves run between the intercostales interni and intimi after they have given off branches described.

laving arrived at the anterior extremity of the osseous rib, each r e, still internal to the internal intercostal muscle, passes inwards ts deep surface, lying at first upon the parietal pleura, and sublently upon the sterno-costalis muscle, crossing in its course the rnal mammary vessels. On reaching the side of the sternum it es straight forwards, to become an anterior cutaneous nerve, cing in succession the following structures: the interchondral ion of the internal intercostal muscle; the anterior intercostal ibrane; the pectoralis major muscle; and the deep fascia.

Branches.—These are muscular, lateral cutaneous, and anterior ineous.

The muscular branches supply the following muscles: the levatores arum, serratus posterior superior, subcostal muscles, intercostal internal mammary artery; AOR, aorta; RA, anterior primary ramus of thoracic spinal nerve; COLL, collateral branch; LC, lateral cutaneous branch; P, anterior terminal perforating, passing in front of internal mammary.

scles, the sterno-costalis, the serratus posterior inferior, and the scles of the anterior abdominal wall.

The lateral cutaneous nerves arise just beyond the costal angles, 1 run as described above. They pierce the external intercostal scles, and make their appearance under fibrous arches connecting costal slips of origin of the serratus anterior. The first intercostal ve, as a rule, gives off no lateral cutaneous branch, and that of the ond is known as the intercosto-brachial nerve.

The anterior cutaneous nerves are the terminal branches of the upper intercostals, that of the first being sometimes absent. For their

criptions, see Index.

Intercostal Arteries. — These vessels are arranged in two sets derior and anterior.

Posterior Series. — The intercostal arteries of the first two spaces ! derived from the superior intercostal artery (see Index). The intercostal arteries of the lower nine spaces are branches of the < scending thoracic aorta, and are called the posterior intercostal arten Each at first lies between the posterior intercostal membrane and 1 parietal pleura. About the level of the angle of the rib it pierces i posterior intercostal membrane, and gives off its collateral intercos branch, which inclines downwards. These two arteries now p; forwards between the two intercostal muscles, the main poster intercostal lying in the costal groove of the upper rib, where it 1 the intercostal vein above it and the intercostal nerve below it, a the collateral intercostal lying along the upper border of the lov rib. These two vessels, in the case of the upper nine spaces, termin; by anastomosing with the anterior intercostal arteries, which are t in number in each of these spaces, and will be presently describi These anastomoses take place a little in front of the mid-point betwe the vertebral column and the side of the sternum.

Branches.—These are posterior, collateral intercostal, and late cutaneous.

The posterior branch passes backwards to the muscles and inte^ ment of the back, giving off in its course a spinal branch, which ent< the vertebral canal through the intervertebral foramen.

The collateral intercostal branch, as stated, arises about the le^ of the angle of the rib, and inclines downwards to the upper border the lower rib, along which it passes between the intercostal muscles.

The lateral cutaneous branch accompanies the corresponding latei cutaneous nerve.

The posterior intercostal and collateral intercostal arteries gi branches to the intercostal muscles and ribs. Those of the thii fourth, and fifth spaces, at least, furnish branches to the mamma gland and pectoral muscles, anastomosing with the thoracic brand of the acromio-thoracic artery from the first part of the axillary, a with the lateral thoracic from the second part of that vessel. T first posterior intercostal artery, as it enters the third intercostal spa< gives off a branch which ascends to the back part of the second int< costal space, and anastomoses with the branch of the superior intercos artery to that space.

Anterior Series. — The internal mammary artery furnishes t' anterior intercostal arteries to each of the upper six intercostal spac and the musculo-phrenic branch of the internal mammary furnisl two anterior intercostal arteries to each of the seventh, eighth, a ninth intercostal spaces. The arteries of the upper six spaces lie first upon the sterno-costalis muscle, and then upon the parietal pleu being under cover of the internal intercostal muscle. Afterwards the anterior intercostal arteries pass between the external and inter] intercostal muscles. In each space they anastomose with the poster intercostal and collateral intercostal arteries, and also with the c responding intercostal arteries of the upper two spaces.

Branches.—These are distributed to the intercostal muscles, ri mammary gland, and pectoral muscles.



The lower two intercostal spaces are not furnished with anterior srcostal arteries. The posterior intercostal arteries of these spaces, sr leaving them, enter the abdominal wall, and pass forwards ween the internal oblique and transversalis muscles to the rectus lominis, in which they anastomose with the superior epigastric 1 inferior epigastric arteries.

Intercostal Veins.—These veins accompany the corresponding


enes. The posterior intercostal vein passes backwards in the costal iove of the upper rib in company with the posterior intercostal ery, above which it lies. In the region of the angle of the rib it is ned by the collateral intercostal vein , which accompanies the corremding artery. Close to the vertebral column the posterior intercostal n receives a large posterior branch, which returns blood from the iscles and skin of the back, the vertebral venous plexus, and the -tebral canal. The mode of termination of the posterior intercostal ns differs on the two sides, and will be described in connection

h the dissection of the posterior wall of the thorax. The anterior intercostal veins accompany the anterior intercostal cries. Those of the upper six intercostal spaces pass to the internal immary, and those of the succeeding three spaces pass to the musculo

renic veins.

Intercostal Lymphatics.—The lymphatic vessels of the intercostal ices pass partly to the posterior intercostal glands, which lie at the ck parts of the intercostal ices, and partly to the anter intercostal or sternal glands, rich lie along the course of 3 internal mammary artery.

Internal Mammary Artery.— ris vessel arises from the lower .e of the first part of the bclavian artery, and passes wnwards, forwards, and inirds behind the inner part of 3 clavicle and the first costal F IG - 580. To show the Interrelations

of the Right Internal Mammary Artery and Phrenic Nerve, and their Relations to Subclavian and Innominate Veins (Interrupted Lines) and to Pleura.


AP, anterior margin of pleura (PL). The mediastinal surface is stippled.


rtilage. It then descends verbally behind the succeeding stal cartilages as low as the

th intercostal space, where it minates by dividing into two anches—namely, the superior igastric and the musculorenic. The artery lies about ■§ inch from the margin of the sternum.

Cervical Relations— Anterior. —The clavicular portion of the sternoistoid muscle, and the internal jugular and subclavian veins. The aenic nerve crosses it superficially from without inwards. Posterior. The dome of the pleura.


Thoracic Relations — Anterior. —The pectoralis major; upper costal cartilages; anterior intercostal membrane; internal intercos muscles; and upper six intercostal nerves. Posterior. —The plei above, and subsequently the sterno-costalis muscle. Lateral .—1 artery has a vena comes on either side of it. The anterior intercos or sternal glands lie along the course of the vessel.

Branches. —The artery gives off no branches in the neck. In i thoracic part of its course it furnishes the following branches:


Pericardiaco-phrenic.

Mediastinal.

Pericardial.

Sternal.


Anterior intercostal. Perforating. Musculo-phrenic. Superior epigastric.


The pericardiaco-phrenic artery , long and slender, arises high up, a accompanies the phrenic nerve to the diaphragm. It gives twigs the pericardium and pleura, and in the diaphragm it anastomoses w the phrenic branch of the abdominal aorta and with the muscr phrenic branch of the internal mammary. The mediastinal branc are distributed to the contents of the mediastinum—namely, remains of the thymus body, mediastinal glands, and areolar tiss The pericardial branches supply the front part of the pericardium. 1 sternal branches are distributed to the sternum and the sterno-cost; muscle. The anterior intercostal arteries . are two in number to each the upper six intercostal spaces. For their description, see Ind The perforating branches are six in number, one arising opposite e£ of the upper six intercostal spaces. Each vessel pierces the inter intercostal muscle, anterior intercostal membrane, and pectoralis maj It then gives a few twigs to the front of the sternum, and turns o wards to supply the skin of the pectoral region. The second, thi fourth, and fifth perforating branches give offsets to the inner port; of the mammary gland.

The musculo-phrenic artery is one of the terminal branches of 1 internal mammary. It arises from that vessel in the sixth intercos space, and passes obliquely downwards and outwards behind 1 seventh, eighth, and ninth costal cartilages. About the level of 1 tenth rib it perforates the diaphragm, and terminates in the late wall of the abdomen, where it anastomoses with the ascending brar of the deep circumflex iliac artery. It gives off anterior intercos and muscular branches. The anterior intercostal arteries are two number to each of the seventh, eighth, and ninth intercostal spac in which they are disposed in a manner similar to the anterior intercos branches of the internal mammary. The muscular branches c distributed to the diaphragm and lateral wall of the abdomen, the diaphragm they anastomose with the phrenic branch of t abdominal aorta and the pericardiaco-phrenic branch of the interi mammary.

The superior epigastric artery is the other terminal branch of i internal mammary, of which it is the continuation. It descer


nd the seventh costal cartilage, and passes through the areolar val between the sternal and costal portions of the diaphragm. In manner it enters the sheath of the rectus abdominis, lying at first nd the muscle, but afterwards entering it. In the muscle it tomoses with the inferior epigastric artery, which is a branch of external iliac.

'he branches of the superior epigastric artery will be found deed on p. 731.

'he internal mammary veins (venee comites) are two in number, lie one on each side of the artery. They are formed respectively


Sterno-hyoid Muscle Sterno-thyroid Muscle.


Fig. 581. —Dissection of the Anterior Wall of the Thorax (Posterior View).


The union of the venae comites of the musculo-phrenic and superior astric arteries. In their course they receive tributaries correspondto the branches of the artery. About the level of the first rcostal space the outer vein crosses over the artery and joins the r vein to form a single vessel, which opens into the corresponding 'inmate vein. The internal mammary veins are provided with ns at intervals.

►ternal or Internal Mammary Lymphatic Glands. —These glands } a chain along the internal mammary vessels. They are usually ined, however, to the first three spaces, there being one, or it may be two, in each of these spaces. They usually lie in front of the inter mammary vessels.


They receive their afferent vessels from (i) the inner third of mammary gland, (2) the anterior half of the costal pleura, (3) anterior halves of the external and internal intercostal muse (4) the lymphatics which accompany the superior epigastric arte and (5) the anterior group of superior diaphragmatic glands. T 1 efferent vessels pass to the thoracic duct , or to the right lymphatic d\ according to the side on which the glands lio. Frequently one more of these vessels drain to the supraclavicular group of gland? fact which explains the infection (which sometimes occurs) of th glands in malignant disease of certain abdominal viscera.


Sterno-costalis (Triangularis Sterni) — Origin. —(1) The deep surf; of the xiphoid process and body of the sternum close to the late border, and extending as high as the level of the third costal cartila and (2) the deep surfaces of the lower two or three true costal cartila at their sternal ends.

Insertion. — The deep surfaces and lower borders of the co? cartilages from the sixth to the second. The insertion takes pi by separate slips, and one or two of the upper slips may be partk attached to the rib itself.

Nerve-supply. — The intercostal nerves of the adjacent spaces.

The lowest fibres of the muscle are horizontal; the succeeding fit pass obliquely upwards and outwards; and the upper fibres are aim vertical.

Action. — To depress the anterior extremities of the ribs, and take part in expiration. It fixes the anterior part of the chest w and so assists the actions of the muscles, particularly those of pectoral group, attached to that region.

The muscle forms a thin musculo-tendinous sheet, which is situa on the deep surfaces of the costal cartilages and side of the sterni and is serially continuous with the transversalis abdominis mus< It supports the internal mammary vessels, sternal glands, and cert of the intercostal nerves, whilst its deep surface rests upon the park pleura.


Thoracic Cavity

Contents and their General Position. — The thoracic cavity is chk occupied by the lungs and heart. The lungs are situated one in e; half of the cavity, and each lung is provided with a serous membra called the pleura. The heart lies obliquely between the lungs, project more to the left of the sternum than to the right, and is enclosed wit a fibro-serous sac, called the pericardium. Each lung is free to exp; except at the hilum, which is situated on its inner surface. Throi this hilum the bronchus, pulmonary artery, and pulmonary v( pass, along with other structures, and the pedicle so formed is ca the root of the lung. The upper part, or apex, of the lung rises i the root of the neck, where it is covered by the cupola of the plei

in turn being covered by the suprapleural membrane. The lower , or base, of the lung rests upon the corresponding half of the hragm, the heart lying upon the central tendon of that muscle, rhe two pleural sacs fill the spaces enclosed by the ribs of their sides, but an interval exists between them; this is the mediastinum s. 582 and 583). Nearly all the contents of the thorax (other than lungs and pleurae) lie in the iastinal space, which, as will be ., is arbitrarily divided for conience and description, rhe pulmonary artery springs a the base of the right ventricle

he heart, and the aorta from base of the left ventricle. The innominate vein courses along upper aspect of the arch of the

a in front of the origins of the )minate, left common carotid, left subclavian arteries, and

es with the right innominate 1 behind the sternal end of the

right costal cartilage to form superior vena cava. This latter sel opens into the posteroerior angle of the right atrium he heart, and, just before piercthe pericardium, receives the a azygos which arches forwards r the right bronchus. The inor vena cava, having entered thorax through the foramen for a cava in the central tendon the diaphragm, almost lmmetely opens into the postero:rior angle of the right atrium of heart.

The phrenic nerve on each side cends in front of the root of lung, and is intimately related the pericardium, especially on left side. The small anterior monary plexus of nerves lies in

it of the root of each lung. The vagus nerve on each side descends ind the root of the lung, and forms in that part of its course the ch larger posterior pulmonary plexus. The following important ves descend in front of the arch of the aorta: the left phrenic, the vagus, the superior cervical cardiac branch of the left sympathetic, !■ the lower cervical cardiac branch of the left vagus. The left


LEADING TO A COSTOPHRENIC SUL cus of Pleura (Dotted Line).

TH is placed in the mediastinum between the pleural sacs.



superior intercostal vein lies in front of the back part of the a arch, usually intervening between the phrenic in front and the v behind. The superficial cardiac plexus of nerves lies within concavity of the arch of the aorta, and the deep cardiac plexus behind the arch and in front of the trachea close to its bifurcc into the two bronchi. The left recurrent laryngeal nerve p; backwards under the arch, and then ascends behind it. Within concavity of the aortic arch the trunk of the pulmonary artery bn up into its right and left divisions, and the ligamentum arterioi extends from the root of the left pulmonary artery to the back ] of the concavity of the aortic arch immediately beyond the origii the left subclavian artery; the recurrent laryngeal nerve winds ro its left side prior to passing upwards behind the arch of the ao The gangliated trunk of the sympathetic lies very deeply, and desce



Fig. 583 — Diagrams showing, in the First Figure, how the Mediasti IS SIMPLY THE INTERVAL BETWEEN THE TWO PLEURAL SACS, A DEFINI WHICH HOLDS EVEN WHEN, AS IN THE SECOND FIGURE, IT IS MUCH TENDED BY PERICARDIUM, ETC.


The lower figure shows how the space between the pleural sacs can be div into a superior (S) mediastinum and an ‘ inferior ’; this term, howeve not commonly used, the lower space being subdivided, by the subver planes of the front and back walls of the pericardium, into a posterior (J middle (M), and a rather doubtful anterior space.


the heads of the ribs close behind the parietal pleura, and the or three splanchnic nerves lie obliquely on the sides of the bodies ie lower thoracic vertebrae.

The oesophagus lies in contact with the front of the vertebral mi, and the trachea is anterior to it. The descending thoracic a lies very deeply, being situated at first on the left side of the T>ral column, but subsequently in front of it. The thoracic duct ads on its right side, and the vena azygos ascends on the right of the thoracic duct, both structures being under cover of the )hagus. The superior and inferior venae hemiazygos, upper and

r, as well as the two transverse azygos veins, upper and lower, fiosely related to the vertebral column.

'he thoracic cavity contains the following sets of lymphatic glands : anterior mediastinal or anterior group of superior diaphragmatic ds in front of the pericardium; the superior mediastinal above pericardium, along the arch of the aorta and innominate veins; posterior mediastinal behind the pericardium; the posterior rcostal in the back parts of the intercostal spaces; and the bronchial tie interval between the diverging bronchi, and also at the root ach lung. In early life a portion of the thymus body, which is l of large size, lies behind the upper part of the sternum, whence fiends into the lower part of the neck.

fleurse. —The pleurae are the two serous sacs which invest the

s, and line the adjacent parietes. Each forms a closed sac, which uite distinct from its fellow. Like other serous membranes, the ra consists of two portions—parietal and visceral—which, however, continuous with one another.

rhe parietal pleura lines the parietes, and is divisible into five ions—namely, costal, diaphragmatic, pericardial, cervical, and iastinal. The costal pleur alines the inner surfaces of the ribs and rnal intercostal muscles. The diaphragmatic pleura covers the er surface of one half of the diaphragm. The pericardial pleura 1 intimate contact with the pericardium, the phrenic nerve and •mpanying vessels alone intervening. The cervical pleura forms t is known as the cupola (dome ), and rises into the neck for about ch above the clavicle, being a little higher on the right side than file left, on account of the projection formed by the liver. The iastinal pleura of each side bounds the mediastinum. rhe viscera pleural closely invests the lung, and is known as the nonary pleura. It is intimately connected with the lung substance, extends into the fissure, or fissures, which map out the lung into s. Below the root of each lung it forms a fold, called the pulmonary went, which descends to the diaphragm; medianly the fold is icted in front on to the pericardium, and behind on to the cesogus..

Continuity and Reflections of the Pleura —(1) In the Transverse action .—Commencing at the deep surface of the sternum, the etal pleura of each side passes backwards to the pericardium, the two being in contact except for a little inferiorly. They form lateral boundaries of the space which is called the anterior mediastin When they reach the pericardium the two pleurae separate, each keep to its own side of that sac, and so forming the pericardial plei which bounds laterally the space known as the middle mediastin Each pleura in this manner reaches the anterior aspect of the i of the corresponding lung, where it becomes the visceral pleura. 1 covers the front of the root of the lung, and then invests the en organ, dipping into its fissure or fissures, as the case may be, and gi\ a covering to the posterior aspect of the root. On leaving the b of the root of each lung, the two pleurae pass backwards slightly c the pericardium, trachea, and oesophagus, and over the descenc thoracic aorta, to the lateral aspects of the bodies of the thor; vertebrae. These portions form the lateral boundaries of the sp which is called the posterior mediastinum. From the vertebral coir each pleura passes outwards over the gangliated trunk of the sypathetic, and then lines the inner surfaces of the ribs, as well as internal intercostal muscles. In this manner it reaches the d surface of the sternum.



Fig. 584. —Schemes to show Pleural Conditions above, through, BELOW THE ROOT OF LUNG (L). P, parietal pleura; V, visceral pleura.


From the foregoing description it will be evident that the plei in passing from the deep surface of the sternum to the vertebral colui meets with, and is reflected over, the lung and its root. At the If of the manubrium sterni the pleura passes uninterruptedly backwa to the vertebral column. That of the right side passes over the 1 of the superior vena cava, innominate artery, right innominate v and trachea; whilst that of the left side passes over the side of left common carotid and left subclavian arteries, (esophagus, ; thoracic duct. The two pleurae, as they pass backwards at this le form the lateral boundaries of the space which is called the supe\ mediastinum.

Below the level of the root of the lung the antero-posterior reflect of the pleura is complicated by a triangular fold, called the pulmon ligament. This fold consists of two layers of pleura in close apposition

h are continuous superiorly with the anterior and posterior pleural stments of the root of the lung. It extends, on the one hand, veen the lower border of the root of the lung and the diaphragm i vhich latter it is attached, and, on the other hand, between the cardium and the inner surface of the lung below the level of the

. In the last-named situation its two layers separate to encase lung at that level. Its lower border is free and concave.

[2) In the Vertical Direction.—Superiorly the parietal pleura of 1 side rises in the form of a cupola into the root of the neck for about ch above the clavicle, where it is covered by suprapleural membrane sons fascia). This fascia is derived from the scalene group of teles, and is attached, on the one hand, to the medial border of the rib, and, on the other, to the front of the transverse process of the



Fig. 585. — Diagram showing the Reflections of the Pleurae (Transverse Section).


Hith cervical vertebra. The subclavian artery and innominate 1 are intimately related to the cupola of the pleura internally and eriorly, the artery being the higher of the two. Immediately in it of the artery the phrenic and vagus nerves and the internal umary vessels lie in contact with the pleura. Inf eriorly the ietal pleura of each side is reflected from the thoracic wall on to upper surface of the corresponding portion of the diaphragm, ch it covers where the base of the lung rests upon it. The intering portion of the diaphragm (central tendon) is covered by the )us portion of the pericardium. Medially the diaphragmatic pleura omes continuous with the mediastinal pleura.

Lines of Reflection of the Pleurae — Sternal Reflection.- —Behind the lubrium sterni the right and left pleurae are separated from each er by an interspace which represents the superior mediastinum .


At the level of the junction of the manubrium and body of the steri they meet each other, and descend behind the body of the bon close contact and inclining slightly to the left of the median line, the level of the lower border of the fourth costal cartilage the pleura parts company with the right, and passes outwards downwards close to the left border of the sternum, and in intin


Fig. 586. — Surface Markings on Front of Thorax.

Thick black lines mark pleura; dotted lines within these show lungs and ' fissures; fine lines heart and main vessels and lower edge of liver medi interrupted line shows transpyloric plane.

relation with the pericardium. There is, however, a small triang area of that sac which is uncovered by the pleura, and lies in di relation to the anterior thoracic wall. The left pleura continues downward course as far as the inner surface of the sixth costal cartil lying not far from the left border of the sternum. At this leve again passes outwards and downwards, to be reflected on to diaphragm. The right pleura pursues an undeviating course downw;


nd the sternum as far as the junction of the body and xiphoid ess. At this level it leaves the bone, and passes obliquely outwards, iwards, and backwards over the inner surface of the seventh costal lage, from which it is reflected on to the diaphragm.

'osto-diaphragmatic Reflection .—The level of this reflection may be idered, in the first place, as it affects certain definite vertical lines, he left sternal line it takes place at the level of the sixth costal


Fig. 587. — Surface Markings on Back of Thorax.

ira, thick line; lungs and fissures, dotted lines within these; uppermost level of diaphragm and liver on right side, interrupted line, hirst, sixth, and twelfth thoracic spines marked. Roots of lungs indicated.

tilage, and in the right sternal line at the level of the seventh costal tilage. In the left mammary line it takes place at the level of the ith costal cartilage, where it joins the osseous part of the rib, and the right side at a similar level. In the left mid-axillary line it es place on a level with the lower border of the tenth rib, this being lowest point to which the pleura descends. In the right midllary line it takes place on a level with the upper border of the tenth , or, it may be, the lower border. Posteriorly, in the scapular line




(inferior angle of the scapula) on each side it takes place at the k of the lower border of the twelfth rib. From this point inwards the vertebral column the line of pleural reflection is a little below adjacent border of the twelfth rib, and is very nearly midway betw the vertebral end of that rib and the first lumbar transverse proces

From the foregoing description it will be evident that the pie descends lowest in the mid-axillary line, and that posteriorly, d to the vertebral column, it actually descends below the level of lower border of the twelfth rib. The direction of the line of cos diaphragmatic reflection, from before backwards, is at first obliqr downwards and outwards until the level of the tenth rib is reach The line then passes backwards and upwards to the vertebral colui The costo-diaphragmatic pleural line is on a distinctly lower le than the margin of the base of the lung, but it is a little above the ] of the costal attachment of the diaphragm. The portion of diaphragm below the line is therefore in direct contact with the thoiz wall and adjacent internal intercostal muscles, without the intervent of the pleura, and the costo-diaphragmatic reflection is connected these structures by a fascial expansion.

The free surfaces of the parietal and visceral pleurae are in hea in close contact. They are polished, and moistened by a slight amoi of serous fluid, so that they glide smoothly upon each other. In ca of pleurisy, however, certain changes take place. The free surfa become roughened by the deposit of lymph, and the movement of lung is accompanied by the sound known as pleuritic fricti Adhesions are also frequently formed, and a serous exudation tai place into the pleural sac, which tends to compress the lung injurious the condition being known as pleurisy with effusion. In cases serous exudation the cavity of the pleura, which is a shut sac, is clea demonstrable, but in health no such cavity exists, the parietal a visceral pleurae being at all times in intimate contact with each oth The attached surfaces of the parietal and visceral pleurae are rougher by fibrous processes, by means of which they are connected to 1 parts which they cover.

The costal pleura is the thickest, and can readily be stripped fr< the inner surfaces of the ribs and internal intercostal muscles. Tb is a fairly thick layer of subserous areolar tissue on its attached surfa The diaphragmatic and pericardial pleurae are thinner than the cos pleura, and are more adherent to the subjacent structures. 1 diaphragmatic pleura follows closely the upper surface of the diaphraj in its antero-posterior curvature, with the result that though in 1 mammary line it is attached anteriorly to the eighth costal cartila it ascends when traced backwards to the level of the fifth costal cartik prior to turning downwards to the level of the twelfth rib. 1 pulmonary pleura is the thinnest and most adherent. Beneath there is a layer of subserous areolar tissue containing much elas tissue, and this is in continuity with the areolar tissue which perva( the lung.


Differences between the Two Pleural Sacs. —The right pleural sac rises higher

he root of the neck, and is shorter and wider than the left. These differences ue partly to the projection formed by the liver on the right side, and partly 3 greater inclination of the heart to the left of the sternum than to the right.

Ilood-supply. —The parietal pleura receives its arteries from the rior and posterior intercostals, and from the various branches of internal mammary. The visceral pleura receives its blood from bronchial arteries.

'he veins pursue courses corresponding to the arteries, ferve-supply. —The nerves are derived from the sympathetic, nic, vagus, and intercostal nerves.

lymphatics—Visceral or Pulmonary Pleura. —The lymphatic vessels lis part of the pleura open into the superficial lymphatics of the s. Parietal Pleura. —The lymphatics of the costal pleura open the lymphatics of the internal intercostal muscles , which terminate ) the sternal or internal mammary glands, and (2) the intercostal ds. The lymphatics of the diaphragmatic pleura open into the )hatics of the diaphragm. The lymphatics of the mediastinal pleura into (1) the anterior mediastinal glands, and (2) the posterior iastinal glands.

'here are some costal pleural areas, however, which have particular lages. The ‘ apical ’ or cervical pleura, including that part below niddle of the first rib, drains into glands in the bottom of the neck, nd the lower end of the jugular, or it may be into the subclavian k; occasionally it seems to have some drainage into the uppermost of the axillary glands. Just below this area, and extending 1 to about the fourth rib, is a second region which, beside the lary drainage into posterior intercostal and internal mammary ds, usually has some drainage through the thoracic wall into the ary glands, accompanying the lateral intercostal nerves and vessels, drainage into axillary glands may even (but unusually) extend down r as the sixth rib.

iructure. —The pleura is a typical serous membrane like the serous portion le pericardium, the peritoneum, and the tunica vaginalis. Such mem*s are called serous because their free surfaces are moistened by a small tity of serous fluid. Briefly stated, the pleura consists of a homogeneous, sctive-tissue basement membrane, containing elastic tissue, and lined endothelium.

evelopment. —The pleura is developed from the walls of the coelom, or -cavity, which is the cleft in the mesoderm separating the splanchnopleure >omatopleure (see p. 78).

'he Mediastinum. —The mediastinum is formed by the approxion of the two pleural sacs in the region of the median anteroerior line of the thorax. The interval between the two sacs is d the mediastinal space , and its boundaries are as follows: in front, sternum; behind, the bodies of the thoracic vertebra; and on either the corresponding pleural sac. The mediastinal space contains dures so numerous as to necessitate its subdivision into four parts perior, anterior, middle, and posterior.


Fig. 588. —Mediastinal Contents exposed by pulling back the Ante

Parts of the Pleural Sacs.

Smaller mediastinal vessels are not shown.

and laterally, the mediastinal pleura of each side as it extends from deep surface of the manubrium sterni to the vertebral column.

Contents.—These are as follows: (1) the arch of the aorta; (2) innominate artery, and the thoracic portions of the left common car and left subclavian arteries; (3) the right and left innominate ve and the upper half, or extra-pericardial portion, of the superior \ cava; (4) the phrenic, vagus, left recurrent laryngeal, and can nerves; (5) the trachea, oesophagus, and thoracic duct; (6) the supe mediastinal glands; and (7) the remains of the thymus.

In studying the topographical anatomy of the thorax it wT


The superior mediastinum is situated above the pericardium, its boundaries are as follows: in front, the deep surface of the manub: sterni, with the origins of the sterno-hyoid and sterno-thyroid mus behind, the bodies of the upper four thoracic vertebrse and the I portions of the longus cervicis muscles; above, an imaginary \ corresponding to the superior aperture of the thorax; below imaginary plane passing from the lower border of the manub: sterni to the lower border of the body of *the fourth thoracic verte


Inf. Thyroid vein L. Innominate V. Thymus

Bulmonary A.


d convenient to use as a landmark the manubrio-sternal joint,

h is often sufficiently superficial to be apparent as a transverse 3 known as the sternal angle (angle of Louis). The angle is in the 3 horizontal plane as the disc between the bodies of the fourth and thoracic vertebrae, and therefore indicates the level of the imaginary e separating the superior from the other divisions of the mediasti. The angle marks the level at which the ascending aorta ends and descending aorta begins: the superior limit of the pericardium-and


L. Vagus N.

L. Phrenic N.

Sup. Intercostal Vein


Recurrent Laryngeal N. going to turn round Lig.


L. Appendix Infundibulum


R. Vagus


Cardiac Nerves

R. Phrenic N. Sup. V. Cav.

Ascending Aorta


Fig. 589. — Main Mediastinal Structures seen from the Front (Heart exposed).


The left side of the heart. At this same level the two pleural sacs meet ront, the trachea bifurcates, the vena azygos enters the superior a. cava, the left recurrent laryngeal nerve winds round the ligaitum arteriosum, the thoracic duct crosses the middle line, and the phagus reaches the middle line.

the anterior mediastinum is situated behind the body of the num, and its boundaries are as follows: in front, the deep surface he body of the sternum, and the left sterno-costalis muscle; behind, pericardium; and laterally, the mediastinal pleura of each side as



it extends from the deep surface of the body of the sternum to lateral aspects of the pericardium. Its direction is downwards an the left. At its upper part there is no interspace, because the pleural sacs come into contact behind the first piece of the bod] the sternum. Below this level, however, the left pleural sac dive: from its fellow, so as to leave an interspace. *

Contents.— These are the anterior mediastinal glands, s< lymphatic vessels, the anterior mediastinal branches of the inte mammary artery, and areolar tissue.



Fig. 590. - Transverse Section of the Thorax through the Sec Sternal Segment in Front and the Body of the Ninth Thor \ ERTEBRA BEHIND, SHOWING THE REFLECTIONS OF THE PLEURAE AND Position of the Viscera.


S. Sternum

A.M. Anterior Mediastinum A. A. Ascending Aorta P.A. Pulmonary Artery R.A.A. Right Appendix R.A. Right Atrium M.M. Middle Mediastinum L.A. Left Atrium


P.M. Posterior Mediastinum O. (Esophagus

D.A. Descending Thoracic Aorta T.V. Thoracic Vertebra M. Middle Lobe of Right Lung R.U. Right Upper Lobe R.L. Right Lower Lobe L.U. Left Upper Lobe L.L. Left Lower Lobe


Anterior Mediastinal Glands. —These glands are situated within areolar tissue of the lower part of the anterior mediastinum, between lower part of the body of the sternum and the front of the pericardii u re f e * ve ^eir a ff went vessels from (i) the antero-median port

ot the diaphragm, corresponding to the xiphoid process of the sternii (2) the supero-anterior surface of the liver on either side of the falcifc ligament (3) the anterior part of the pericardium; (4) the antei P 3 , 1 ^ Pr . e mec hastinal pleura. Their efferent vessels ascend and oj into the internal mammary and superior mediastinal glands.


he middle mediastinum lies behind the anterior and below the rior mediastinum, and is the widest part of the interpleural space, ontents. —These are as follows: (1) the heart, enclosed in the ardium; (2) the ascending aorta; (3) the pulmonary trunk; ie lower half or intrapericardial portion of the superior vena cava ; he phrenic nerves and the pericardiaco-phrenic vessels; (6) the cation of the trachea; and (7) the roots of the lungs, he posterior mediastinum is situated behind the pericardium, and v the posterior part of the superior mediastinum, with which r it is continuous. Its boundaries are as follows: in front , the ardium, and below this the posterior part of the diaphragm;


Fig. 591. — Structures in Posterior Mediastinum, seen from the Left.


id, the bodies of the thoracic vertebrae below the level of the lower ier of the body of the fourth; and laterally, the mediastinal pleura ich side as it extends from the back of the root of the lung to side of the vertebral column.

Contents. —These are as follows: (1) the descending thoracic aorta;

he oesophagus, and the two vagus nerves; (3) the thoracic duct; he vena azygos; (5) the superior and inferior venae hemiazygos, with corresponding transverse azygos veins; (6) the greater splanchnic r es, right and left; and (7) the posterior mediastinal glands.

Phrenic Nerve. —The nerve arises chiefly from the anterior primary sion of the fourth cervical nerve. It usually receives a small root from the anterior primary division of the third cervical, and, a rule, an additional root from that of the fifth cervical. Hat descended on the superficial surface of the scalenus anterior mu: to the root of the neck, it crosses the internal mammary artery su] ficially from without inwards. It then enters the thorax and desce in front of the root of the lung in close contact with the side of pericardium, and under cover of the mediastinal pleura. Ha\ reached the diaphragm, the nerve divides into several branches, wl pierce that muscle, to be distributed to its abdominal surface, terminal branches of each nerve are connected in the diaphragm v filaments of the corresponding phrenic plexus of the sympathe which is an offshoot from the coeliac plexus. At the place of junct

of the two sets of fibres on right side there is a small gangli called the phrenic ganglion. the thorax the phrenic ne occupies the superior and mid mediastinal spaces. The n phrenic nerve lies in success on the outer side of the ri innominate vein and superior v< cava, and then descends in fr< of the root of the right lu Certain filaments from this ne not infrequently reach the un surface of the diaphragm passing through the vena ca aperture. The left phrenic ne: descends in the interval betw< the left common carotid £ left subclavian arteries, where crosses the vagus nerve fr without inwards. It then pas behind the left innominate vc and crosses over the arch of aorta separated from the vagus by the left superior intercostal ve after which it descends in front of the root of the left lung. E; nerve is accompanied by the pericardiaco-phrenic artery, which i branch of the internal mammary artery.

Branches.— The nerve of each side furnishes twigs to the p< cardium, the mediastinal pleura, the inferior vena cava, peritonei liver, and suprarenal glands; its principal branches are, howet distributed to the diaphragm.

Differences between the Two Phrenic Nerves. —(i) The right nerve is shoi, than the left, because the right half of the diaphragm, having the bulk of liver below it, is higher than the left half. (2) The right nerve is straighter til the left, because the heart, enclosed in the pericardium, projects less to the ri side than to the left. (3) The right nerve occupies a deeper position in the upl part of the thorax than the left. " }


Fig. 592. — Structures in Posterior Mediastinum, seen from the Right.

PH.N., phrenic nerve.


Pericardium. — The pericardium is the fibro-serous sac which loosely ounds the heart in the middle mediastinum. It is somewhat cal, being wide below, where it is in contact with the diaphragm, narrow above, where it surrounds the great vessels connected 1 the base of the heart. On each side it is intimately related to mediastinal pleura, and is embraced by the anterior portions of inner surfaces of the lungs. The phrenic nerve on each side descends ery close contact with it. In front of it are the body of the sternum the sternal ends of the corresponding costal cartilages. Its anterior ace is to a greater or less extent encroached upon by the adjacent


Fig. 593. — The Heart (Anterior View) and Pericardium. The anterior part of the pericardium has been removed.


•tions of the anterior margins of the lungs and by the two pleurae, ere is, however, a small portion of this surface which is immediately ited to the sternum below the level of the lower border of the fourth

costal cartilage at its sternal end. Posteriorly, the pericardium in front of the posterior mediastinum, and the oesophagus is here ited to it opposite the posterior aspect of the left auricle of the heart. The pericardium consists of two portions—an external or fibrous, I an internal or serous. The fibrous pericardium is strong and dense, eriorly it is attached to the middle lobe of the central tendon of ! diaphragm, and slightly to its muscular part, more particularly on the left side. Superiorly it ensheathes the great vessels connec with the base of the heart, with the single exception of the infei vena cava.

The fibrous layer is attached to the sternum by two fibrous ban which are known as the superior and inferior sterno-pericara ligaments of Luschka, the former being attached to the deep surf; of the manubrium, and the latter to the deep surface of the xiph process.

The serous pericardium is a typical serous membrane, and consi of two layers, parietal and visceral, which together form a closed sa

The parietal portion lii the inner surface of 1 fibrous part, to which it closely adherent, and a intimately covers the up] surface of the central tend of the diaphragm.

The visceral portu known as the epicardiu closely invests the heart, a! also the great vessels at base more or less complete The continuity between t parietal and serous portic is established inferiorly alo the inferior vena ca^ Superiorly the continuity established along the gre vessels at the base of t heart about ij inches abo it. In this situation t serous portion forms an c terial sheath which enclos within it the ascending aor and pulmonary trunk 1 about ij inches, this bei the only complete shea formed by the serous portic Behind this sheath, with its contents, and in front of the atrial port! of the heart, there is a passage, called the transverse sinus of t pericardium, which leads from the right to the left side of the sero sac. The serous portion is also related to the superior vena cava ai the pulmonary veins, but it only covers them in front and at t sides.

The serous portion of the pericardium forms a triangular fo, called the ligament of the left vena cava (vestigial fold of Marshal

which is situated between the left pulmonary artery and the upper 1< pulmonary vein. Its base is directed towards the left, and its surfac


Fig. 594. —Scheme of Disposition of Arterial (A) and Venous Mesocardia (V) on Posterior Wall of Pericardium.

The dotted arrow lies in transverse sinus.







THE THORAX


1019


anterior and posterior. Between its two delicate layers there is nail fibrous cord, a vestige of the left duct of Cuvier; this, like the apericardial part of the superior vena cava on the right side,

es down in front of the pulmonary vessels. The free surfaces of the parietal and visceral layers of the serous don are smooth, polished, and lubricated by serous fluid to allow of movement on the part of the heart. In the course of pericarditis y become at first dry, and then roughened by deposits of lymph, s giving rise to the pericarditic friction sound, and, it may be, to esions. They may also become separated from each other by an sion into the pericardial sac.

Blood-supply.—The fibrous portion of the pericardium and the ietal layer of the serous portion receive their arteries from (1) the icardial and pericardiaco-phrenic branches of the internal mammary, (2) the descending thoracic aorta. The visceral layer of the >us portion receives arterial twigs from the coronary arteries of the rt.

The veins pass to the internal mammary, pericardiaco-phrenic, and gos veins.

Nerve-supply.—The phrenic, vagus, and sympathetic nerves. Lymphatics.—These pass to the anterior, superior, and posterior liastinal glands.

Structure. —The fibrous portion of the pericardium is composed of fibrous lie, and is very dense, but not very extensible. The serous portion consists a homogeneous, connective-tissue basement membrane containing some tic fibres, and lined with endothelium. The parietal layer is much thicker n the visceral; the latter is intimately connected with the cardiac muscular ue, except along the grooves, which are occupied by adipose tissue and 3 d vessels.

Development. —The serous portion of the pericardium is developed from walls of the coelom, or body-cavity, which is the cleft in the mesoderm arating the splanchnopleure and somatopleure.

The fibrous walls have various origins; the antero-lateral parts come from deep layers of the body-wall, split off by the extension of the pleural cavities, l the lower or diaphragmatic part is derived from the septum transversum.

} cavity is at first continuous with the pleural sacs, but the openings, which dorsal and medial to the ducts of Cuvier, are closed by the end of the first nth.

The Thymus.—This is present in the foetus and young child, a.nd ms a very conspicuous object in the dissection of a child during J first year or two of life. It attains its greatest size at puberty, er which, as a rule, it slowly atrophies, although traces of it are to found even in advanced age. The atrophic process which it under-S is, however, extremely variable. In its fully-developed condition is situated partly in the thorax and partly in the neck. In the mer situation it occupies the superior and anterior mediastinal ices, extending as low as about the level of the fourth costal cartilages, d lying in front of the great bloodvessels and upper part of the perirdium, the upper part of the sternum being in front of it. In the ck it extends as high as the lower part of the thyroid gland, being


1020


A MANUAL OF ANATOMY


under cover of the sterno-hyoid and sterno-thyroid muscles. In situation it embraces the front and sides of the trachea, complel concealing it from view, and encroaches upon the carotid sheath

either side. Its length is ab


Two Follicles


Trabecula


Medulla


Cortex


Fig. 595. —Transverse Section of a Lobule of the Thymus Gland of a Kitten.


The concentric corpuscles of Hassall are shown in the medulla.


2w inches, and its breadth, wt


is greatest inferiorly, is about inches. Its colour is pinkish is soft in consistence; and surface shows indications of lo lation. It consists of two as} metrical lateral lobes, each of wh is pyramidal. In some cases left lobe is the larger, and other cases the right. These lo are in close contact, but are s quite distinct. Sometimes a th lobe is present, occupying an termediate position between other two.

Blood-supply.—The arteries chiefly derived from the inter mammary, inferior thyroid, s superior thyroid.

The veins open into the rij and left innominate and thyr veins.

Nerve-supply.—The nerves ; derived from the sympathetic a vagus.


Structure. —Each lobe has a capsule of fibrous tissue, from which traben pass into the interior. These trabeculae map out each lobe into large and sn lobules. Each lobule consists of an outer cortical and an inner medull portion. The cortex is composed of lymphoid tissue, the lymphoid elem predominating over the retiform, and it is surrounded by a capillary r work of bloodvessels which contains many lymph corpuscles. The lymph tissue of the cortex is incompletely subdivided into nodules by means trabeculae.

The medulla is more transparent than the cortex, the retiform element the lymphoid tissue is more conspicuous, and the lymph corpuscles are \ numerous. In addition, the medulla contains small groups of cells, more less concentrically arranged, which are known as the concentric corpuscles Hassall. According to one view, these cells are remains of the diverticula fr which the thymus body is developed; but another view is that they are conceri with the formation of bloodvessels and connective tissue.

Development. —The thymus body is developed in two lateral parts from entodermic epithelium of the pharyngeal portion of the primitive gut. 1 epithelium of the third visceral cleft on either side becomes evaginated early the second month, and gives rise to dorsal and ventral diverticula. The vent diverticulum, which forms the thymic growth, has a thick epithelial wall, bu small lumen, and grows in a downward direction. Its distal end, which ] ventral to the pericardium, forms a solid enlargement, and the proximal d loses its connection with the third visceral cleft. The enlarged distal end grj




THE THORAX


1021


umerous solid epithelial buds, which are invested with mesoderm. This ing gradually extends to the proximal part of the diverticulum. The solid and cords of each side ramify freely, and give rise to the corresponding lobe e thymus. The original diverticulum thus assumes a lobulated appearance, resembles a racemose gland. The buds or acini, however, are solid, and not w, as in racemose or acinous glands. The acini are separated by connective s and bloodvessels, which are developed from the surrounding mesoderm, phoid tissue is also developed from the mesoderm around the acini, and tissue forms the greater part of the adult thymus. The epithelial elements ch lobe are subordinate to the lymphoid tissue, and are ultimately represented le concentric corpuscles of Hassall.

jungs.—The lungs are two in number—right and left. They are lgy in consistence, float in water, and are readily compressed, m pressed between the fingers crepitation is elicited, this being to the displacement of air. When the lung is incised, similar litation is heard, and a muco-serous fluid, mixed with air, exudes, y possess considerable elasticity, their colour is that of a dark slate, they are usually mottled, this being due to carbonaceous matter, larly life, however, the colour is rose-pink.

rhe lungs occupy the greater part of the thoracic cavity. Normally / are at all times in close contact with the thoracic walls, the pleurae rvening. Unless adhesions have formed during life between the

eral and parietal pleurae, the surface of each lung is quite free spt in two situations—namely, at the root, which occupies a limited i of the inner surface, and at the attachment of the pulmonary ment. Each lung is conical, the base being directed downwards. >resents for consideration an apex, a base, two surfaces, and two iers.

The apex is blunt, and rises out of the thoracic cavity into the t of the neck for about inches. It is here covered by the cupola he pleura, and a little below its highest point it presents a groove its medial and anterior aspects. In the case of the right lung > groove is produced by the innominate and right subclavian arteries, l in the case of the left lung by the subclavian artery of that side, ow this groove there is another groove, produced on either side by innominate and subclavian veins.

The base is extensive, semilunar in outline, and concave in adaptai to the upper arched surface of the diaphragm, upon which it ts, with the intervention of the pleura. The base of the right g is related to the right lobe of the liver, and that of the left lung [he left lobe of the liver, the stomach, and the spleen, the diaphragm srvening in each case. The margin of the base is thin and sharp, 1 it extends into the costo-diaphragmatic recess, reaching lowest lind, but nowhere as low as the line of the costo-diaphragmatic ection of the pleura.

The costal surface is extensive and convex, and in health it is sely applied to the inner surfaces of the ribs and of the internal ercostal and subcostal muscles.

The medial surface is of much more limited extent than the outer


1022


A MANUAL OF ANATOMY


Fig. 596.—Mediastinal Aspect of Right Lung.


part (DA) of the aortic groove, vertically placed and produced 1 the descending thoracic aorta. Anterior to the lower part of tf groove the left lung is related to the oesophagus, but less intimate than the right lung. The inner surface of the right lung presen above the level of the hilum grooves for the following structures: tl vena azygos (AZ), the superior vena cava (SVC) and right innomina vein, the innominate artery, the trachea (T) and oesophagus. Tl inner surface of the left lung presents above the level of the hilu grooves for the following: the arch of the aorta (A), the left subclavb


(Figs. 596 and 597 )- The greater part of it is concave (P) in adaptat to the heart, enclosed in the pericardium, the concavity being grea in the case of the left lung on account of the projection of the he to the left side. About the junction of the anterior two-thirds c posterior third this surface presents a vertical fissure, called the hilt at which the root of the lung is situated. The medial surface of right lung, behind the hilum, is related ((E) to the oesophagus, and corresponding portion of the inner surface of the left lung prese


CE

p

ivc

A R




THE THORAX


1023


jry (S), the left innominate vein, the oesophagus and thoracic

t ((E) The borders are anterior and posterior. The anterior border is 1 and short, and overlaps the pericardium, more so during inspiral than expiration, but leaving an area of the pericardium uncovered, wn as the area of precordial dulness. The anterior border of right lung keeps behind the sternum as low as the sixth right

al cartilage. The corresponding border of the left lung, beyond lower border of the fourth left costal cartilage, presents a deep


Fig. 597. —Mediastinal Aspect of Left Lung.


laped notch, called the cardiac notch , for the reception of the al portion of the heart enclosed in the pericardium. The posterior ier is elongated, thick, and round, and occupies the groove by side of the vertebral column.

Each lung is divided into two lobes, upper and lower, by an exten> oblique, and deep fissure, which penetrates to the hilum. So ) is this fissure that, unless adhesions have formed, the lung appears onsist of two halves. The fissure commences on the inner surface,

■ the posterior border, about 3 inches below the apex. It then



1024


A MANUAL OF ANATOMY


turns round the posterior border, and passes obliquely downwa and forwards over the outer surface to the basal margin. In case of the right lung the fissure joins the basal margin some li distance from the lower end of the anterior border; but in the c of the left lung the fissure joins the basal margin distinctly fart forwards. A good ready guide to this fissure is the lower bordei the pectoralis major muscle, as it forms the anterior fold of the axi The upper lobe is comparatively small, and includes the ap about the upper 3 inches of the posterior border, the anterior bon and in the case of the left lung practically all that can be ausculta anteriorly. The lower lobe is of large size, and lies behind and be the oblique fissure. It includes the base, the posterior border exc


Fig. 598.—Diagram showing the Heart and Lungs in -Situ.

1. Tricuspid Orifice 2. Pulmonary Orifice 3. Mitral Orifice

4. Aortic Orifice x> Region of Latham’s Circle

the upper 3 inches, and practically all that can be ausculta posteriorly.

By means of the oblique fissure each lung, as stated, is divided ii two lobes. In the case of the left lung the division proceeds no fartf In the case of the right lung, however, there is an additional fissr which extends from near the mid-point of the chief fissure at 1 posterior border horizontally forwards over the outer surface to anterior border. This additional fissure cuts off from the upper 1 ( a triangular or wedge-shaped portion, which is called the middle lo

A fourth or even a fifth lobe may be present on the right side. Tb accessory lobes are usually found in the region of the hilum or of the infeij vena cava. If in the former position, the accessory lobe appears to be due t ! lateral displacement of the vena azygos, which in these cases lies in the obit fissure; if in the latter position, the accessory lobe represents the azygos lob( many animals.






THE THORAX


1025


)ifferences between the Two Lungs.—(1) The right lung has two res and three lobes, whilst the left lung has only one fissure and two 3. (2) The anterior border of the right lung is uninterrupted whilst

of the left lung presents interiorly the cardiac notch. (3) T