Talk:Book - Quain's Elements of Anatomy: Difference between revisions

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Although blood ceases at once to pass through the foramen ovale from the moment of birth, or as soon as the left auricle becomes filled with the blood returning from the lungs, and the pressure ^Yithin the two auricles is equalised, yet the actual closure of the foramen is more tardy than any of the other changes now referred to. It is gradually effected by the union of the forepart of the valvular fold forming the floor of the fossa ovalis with the margin of the annulus on the left side ; but the crescentic margin is generally perceptible in the left auricle as a free border beyond the place of union and not unfrequently the union remains incomplete, so that a probe may be passed through the reduced aperture. In many cases a wider aperture remains for more or less of the first year of infancy, and in certain instances there is such a failure of the union of the valve as to allow of the continued passage of venous blood, especially when the circulation is disturbed by over-exertion, from the right to the left auricle, as occurs in the malformation attending the morbus coeruleus.
Although blood ceases at once to pass through the foramen ovale from the moment of birth, or as soon as the left auricle becomes filled with the blood returning from the lungs, and the pressure ^Yithin the two auricles is equalised, yet the actual closure of the foramen is more tardy than any of the other changes now referred to. It is gradually effected by the union of the forepart of the valvular fold forming the floor of the fossa ovalis with the margin of the annulus on the left side ; but the crescentic margin is generally perceptible in the left auricle as a free border beyond the place of union and not unfrequently the union remains incomplete, so that a probe may be passed through the reduced aperture. In many cases a wider aperture remains for more or less of the first year of infancy, and in certain instances there is such a failure of the union of the valve as to allow of the continued passage of venous blood, especially when the circulation is disturbed by over-exertion, from the right to the left auricle, as occurs in the malformation attending the morbus coeruleus.
==DEVELOPMENT OE THE GENITAL AND URINARY ORGANS==
The development of the permanent genital and urinary organs in birds and mammals, is preceded by the formation of a temporary glandular organ with which the principal parts of both these sets of organs are in their origin connected. These bodies are named the Wolffian bodies, after their discoverer, C. F. Wolff". From this close association of these organs, it becomes necessary to describe their development together.
Fig. 598. — Enlarged View from before op the Left Wolffian Body before the Establishment op the DISTINCTION op Sex (from Farre after Kobelt).
a, a, h, d, tubular structure of the WoliBan bodj ; e, Wolffian duct ; /, its upper extremity ; <y, its termination in .r, the iiro-genital sinus ; h, the duct of Miiller ; i', its upper still closed extremity ; I:, its lower eud terminating in the uro-genital sinus ; I, the mass of blastema for the reproductive organ, ovary or testicle.
PRIMARY FORMATION OP THE URO-GENITAL SYSTEM.
===Wolffian bodies===
The Wolffian bodies occupy a considerable space in the abdominal cavity of birds and mammals from an early period of fcetal life, extending at first from the fifth or sixth protovertebral segments to near the caudal extremity, in the form of two reddish prominent ridges, one on each side of the primitive intestine, and below the protovertebral columns and primitive aortaa. They are thickest in the middle of their length, and taper somewhat at their upper and lower extremities. They consist, when fully formed, of short slightly convoluted tubes running transversely, connected on the inner side with vascular glomeruli, very similar to the Malpighian corpuscles of the permanent kidneys, and leading along the outer border into a tube named the Wolffian duct, which terminates on each side in the cloaca. The Maipighian glomeruli were first discovered by Katlike, who pointed out their vascular structure, and their vessels derived from neighbouring branches of the aorta. The ducts of the Wolffian bodies are found to contain a whitish fluid, and the bodies are believed to perform the glandular office of kidneys during a part of foetal life in the higher vertebrata, and they have accordingly received the name of irrimonlial Iciihieys, a designation which is quite appropriate, as it appears that in fishes and amphibia, they remain as the whole in some, and a part in others, of the permanent kidneys.
Fig. 599. — Human Embryo of from 25 to 28 days, viewed from before the thorax and abdomen opened (from Kolliker after Coste).
0, the eye ; in, the maxillary plate ; mn, the inferior maxillary plate ; h, the second postoral plate ; h, the heart ; w, Wolttiaii bodies and ducts on their outer borders ; I, the liver ; c', the upper and t", the lower limbs ; a, the allantoid pedicle, and on each side of it the umbilical arteries ; i, i, tue upper and lower parts of the intestine of which the middle parts with the vitello-intestinal duct have been removed, leaving the mesentery sti'etched between.
In the human foetus they begin to be formed along with the allantois, at a very early period, probably before the third week, as they are already very apparent in the fourth. They have attained their full size by the sixth week, and in the seventh and eighth are rapidly diminishing in size, in connection with the changes which accompany the development of the genital organs and the permanent kidneys.
Fig. 600. — Transverse Section through: the Embryo of the Chick and Blastoderm ON THE Second Day (from Kolliker). d d, hypoblast ; ch, chorda dorsalis ; u w, primordial vertebrae ; m r, medullary plates ; h, corneous layer or epihlast ; u lo h, cavity of the primordial vertebral mass ; in p, mesoblast dividing at s p into h p I, somatopleure, and d f, splanchnopleui'e ; un g, Wolffian duct, beginning in the intermediate cell-mass.
As development advances the "Wolffian bodies rapidly become proportionally shorter and thicker : they shrink towards the lower part of the abdominal cavity, and soon become almost entirely wasted. By the middle of the third month only traces of them are visible in the human embryo.
First origin of the Wolffian bodies. — Difference of opinion has for some time existed among embryologists as to the exact source of the rudiments of the uro-genital system, but it now appears to be fully ascertained by the concurrence of a variety of observers, more especially of Waldeyer, Scheuk, and Balfour, that the Wolffian duct, which is the iirst part formed, and the formative substance of the Wolffian tubes
fig. 601. — Tkaxsverse Section THRotJcn the Abdominal Region of the Chick ok THE Third Day (from Kolliker).
The explanation of the letters is the same as that in the previous figure.
Fig. 602. — Transverse Section of the Embryo-Chick of the Third Day (from Kolliker).
mr, medullary canal and medulla of the spinal cord ; en, notochord ; mch, primordial •vertebral mass ; 7n, muscle-plate ; dr and (//, groove of the primitive intestine as formed by the hyijoblast and splanchnopleure ; cio, one of the two aoi-tte : mw, Wolffian body ; unff, Wolffian duct ; re, vena cardinalis ; h, epiblast ; hp, somatopleure and its reflection into the amnion ; ^^j the p] euro-peritoneal space.
and glomeruli, proceed from the mesoblast, and as these form the foundation of the principal urinary and genital organs, it follows that this system as a wliole has its Inundation in the mesoblastic layer. In birds and mammals the duct, which is first formed, appears in its commencement as a sohd cord in the upper part of a group of cells, projecting below the epiblast, in the interval between the protovertebral mass and the united somatopleure and splanchnopleure of the mesoblast, and thence called the mtermcdiate cell mass (fig. GOO, vnfi). This cord becomes hollow, and gradually changes its place by sinking downwards in the cellular mass in which it is imbedded, towards the pleuro-peritoneal cavity, while the tubular and glomerular structures of the Wolffian body are developed as diverticula from the duct in connection with the neighbouring cellular blastema.
Fig. 603. — Kidneys, Wolffian Bodies, Wolffian and MtJLLERIAN ducts of a foetal bird. Magnified (after J. Miiller).
a, kidney ; 5, tuliular part of Wolfflan body : c, the ovary ; d, suprarenal body \ e, ureter ; /, Wolffian duct ; g, duct of Miiller.
The intermediate cell-mass now forms a considerable projection to the outside of the mesentery, which occupies a median position (figs. 602 and C04), and the epithelium on its surface exhibits a considerable thickening in two places, first, along the inner side, where it becomes columnar, and forms an opaque whitish ridge, the //«'we^;//7itflium, the seat of after formation of the primitive ovigerms ; and second, along the outer side in a line inside the seat of the Wolffian duct, where, by a process of grooved involution, there is gradually formed the duct named Miiller ian, after its discoverer, Johannes Miiller. It is now fully ascertained that both the Wolffian and Miillerian ducts are constantly present in all embryoes of birds and mammals, whatever the sex they may be destined afterwards to assume ; but the respective ducts have a difterent sexual destination, for the duct of ]\lUller becomes converted into the oviduct of the female, while in the male the Wolffian duct forms the vas deferens, or main seminal duct of the testicle ; and while vestiges of the duct of Miiller are perceptible in the developed male, remains of the Wolffian duct are almost always present in the female in a manner afterwards to be described.
The permanent kichicijs of birds and mammals take their origin in connection with the Wolffian duct and formative substance deposited near the Wolffian bodies. Their first rudiments consist in a diverticulum from the upper or dorsal aspect of the Wolffian duct near its posterior extremity, which constitutes the commencement of the ureter ; and from this the tubular and glandular parts of the kidney are formed by extension into the neighbouring mass of blastema at a period somewhat later than that of the development of the Wolffian body itself.
The researches of Waldeyer and others have shown that the procluciive glands of the generative organs in the two sexes, ovary and testis, arise from nearly the same part of the intermediate cell mass, but in a manner somewhat different. Both are mainly produced in the substance which lies along the inner border of the blastemic mass alreadyreferred to, and which may therefore be named the common reproductive blastema ; but with this important difference between them, that in the female the primitive ova originate more immediately from the cells of the surface in the germ ejntheUum, and become afterwards imbedded as Graafian follicles in the deeper substance of the mass which forms a stroma round the ova ; while the glandular substance of the testicle is apparently developed within the cell mass, without any direct concurrence of the superficial or germ epithelium, — which, though at first existing in male as well as in female cmbryoes, and even exhibiting some tendency to the enlargement of some cells as ovigerms (Waldeyer), soon becomes atrophied and reduced in thickness in the male as the structure of the testicle becomes developed.
Fig. 604. — Transverse Section op the Wolffian Body and Rudiment of the Ovary AND THE Duct op Muller in an Embryo Chick at the end of the fourth DAY (from Waldeyer).
WK, Wolffian body ; y, section of the Wolffian duct ; a, germ epithelium with, o, o, cells enlarging into ovigerms ; a', epithelium near the place of involution of MviLler's duct, z ; E, stroma of the ovai-y ; m, mesentery ; L, lateral wall of the abdomen.
The ducts of Muller open at their anterior extremities into the pleuro-peritoneal cavity by the orifice which ultimately becomes the infundibulum and fimbriated ostium abdominale ; and, as their lining membrane has originally been formed by an involution of the epithelium (germ-epithelium) of that cavity, it follows that the lining membranes of the female passages (Fallopian tubes and uterus) which in their later development assume the characters of mucous membrane, and are described as such, have in reality the same origin as the lining membrane of the pleuro-peritoneal cavity.
Fig. 605. — DiAGRAiniATic Outline OF THE Wolffian Bodies in THEIR RELATIONS TO THE EUDIJIENTS OF THE RErRODUcTivE Organs (A. T.).
ot, Seat of origin of the ovaries or testes ; W, Wolffian bodies ; 11', w, Wolffian chicts ; m, m, jVIiillerian ducts ; r/c, genital cord ; iig, sinus iirogeuitalis ; /, intestine ; cl, cloaca.
These ducts at first unite with the Wolffian ducts on each side separately, but later they become separated from them and conjoined at their lower or posterior extremity, and in the development of the female type the uterus results from the further growth of this median or united part, while in the male sex the prostatic vesicle and gland may be looked upon as its nearest representative, and other partial vestiges of the female passages are to be found in the human species and in various degrees in different mammals.
The Wolffian duct, as has already been stated, becomes the vas deferens of the testicle, while the secreting part of the gland, comprising the tubuli seminiferi and the rete testis, are developed in the reproductive blastema of the intermediate cell mass. The union of these two parts of the male organs through the coni vasculosi and the epididymis is brought about by the development of the eflFerent vessels in the upper part, or what may appropriately be termed the sexual part of the Wolffian body, as this structure has been shown by Banks and others to differ from the lower and larger part of the organ by the absence of the vascular tufts or glomerular arrangement in connection ^vith its tubes. The convoluted tubes forming the efferent vessels, which fi-om the time of their first production are in communication with the upper part of the Wolffian duct, become subsequently connected with the vessels of the rete testis, and thus the original Wolffian duct becomes in its upper part the tube of the epididymis, and in its lower the main excretory duct or vas deferens of the testis.
===Homologies of the Wolffian body===
An interesting view of the correspondence of the urino-genital organs in different animals is presented by the recent observations of embryologists on the formation of the Wolffian bodies. It was ascertained by His, Bornhaupt, Rosenberg and Goette, that in the lower vertebrates a second body similar to the Wolffian was formed later in connection with its main duct ; and the researches of Balfour and Semper have shown that in the selachians the permanent kidneys, which had long been believed to be the same with the Wolffian bodies, consist in reality of two sets of tubular organs, of which one corresponds to the Wolffian bodies of the embryoes of the amniota, while the other tubnlar body, already referred to as being of later formation and as connected with the main Wolffian duct, corresponds to the permanent kidneys of the higher animals. Balfour has also ascertained (Jour, of Anat. and Physiol., yoI. x., 1875) that in the selachians both the ducts are found which exist in the amniota, viz., both the Wolffian and the Miillerian ducts, but that they arise in a somewhat different manner from that by which they are produced in birds and mammals, inasmuch as in the selachians the duct of Miiller arises by the formation of a septal partition which divides the original duct through a considerable part of its length into two canals : one of these, the Miillerian duct, is in communication with the pleuro-peritoneal cavity in front, and opens into the cloaca behind as a separate tube ; the other corresponding with the Wolffian, besides being the excretory duct of the primordial kidneys, becomes the vas deferens of the testicle. In the selachians, therefore, the permanent kidneys consist of two parts, of which one, the anterior, is homologous with the temporary kidneys or Wolffian bodies, while the other, or posterior part, corresponds with the permanent kidneys of birds and mammals.
Fig. 606. — Diagram op toe Primitive Uro-genital Organs IN THE Embryo previous TO Sexual Distinction.
The parts are shown chiefly in profile, but the MuUerian and Wolffian ducts are seen from the front. 3, ureter ; 4, urinary bladder ; 5, urachus ; ot, the mass of blastema from which ovary or testicle is afterwards formed ; W, left Wolffian body ; X , part at the apex from which the coni vasculosi are afterwards developed ; w, w, right and left Wolffian ducts ; m, on, right and left Miillerian ducts uniting together and with the Wolffian ducts in g c, the genital cord ; ug, sinus urogenitalis ; ?', lower part of the intestine ; cl, common opening of the intestine and urogenital sinus ; cp, elevation which becomes clitoris or penis ; Is, ridge from which the labia majora or scrotum are formed.
Balfour and Semper have made further the interesting discovery that the transverse tubes of the two parts of the primordial kidney of the lower animals correspond in number and position with the vertebral segments of the region of the embryo in which they are situated, — a fact of great interest in vertebrate morphology, and, according to the authors, leading also to important views of the morphological correspondence of the organs in question with similar organs in the annelida. The tubes of the kidneys in the lower vertebrata are therefore named segmental tiilios, and their common duct (Wolffian), the segmental duct. lu the amniota, however, the same correspondence between vertebrate segments and Wolffian body tubes no longer exists. The External Organs. — The existence in the embryo at first of a single outlet or cloaca, for the urogenital passages and the alimentary canal in common, has already been referred to. This condition of the parts connected with the surface continues even beyond the time when the sexual distinction has begun to become manifest in the deeper organs, as up to the seventh day in the chick and the end of the eighth week in the human foetus. Previous to this time the cloaca presents itself in the form of a Avide cavity, into the middle of which the intestine descends on the dorsal aspect. The pedicle of the allantois opens by a deep groove or recess anteriorly or on the ventral aspect, and on each side there is a widening, into wliich, in succession from the ventral to the dorsal aspect, open the Mullerian and Wolffian ducts and the ureters. The external opening has the form of a vertical slit wider above and below, and is situated in a raised portion of the common integument, from which all the other parts retire more and more within the cavity of the pelvis as it gradually deepens.
Fig. 607. — Development of the External Sexual Organs in the Male AND Female from the Inbifferext Type (from Ecker).
A, the external sexual organs in an embryo of about nine weelis, in which external sexual distinction is not yet established, and the cloaca still exists ; B, the same in an embryo somewhat more advanced, and in which, without marked sexual distinction, the anus is now separated from the urogenital aperture ; C, the same in an embryo of aljoutten weeks, showing the female tj^se ; D, the same in a male embryo somewhat more advanced. Throughout the figures the following indications are employed ; }■)€, common blastema of penis or clitoris ; to the right of these letters in A, the umbilical cord ; p, penis ; c, clitoris ; cl, cloaca ; \({f, urogenital opening ; «, anus ; I s, cutaneous elevation which becomes labium or scrotum ; I, labium ; caudal or coccygeal elevation.
The first change which takes place in the rudiments of the external organs, and which is common to all embryoes, and therefore to botli sexes, consists in the advance from the sides and behind of the partition which separates the intestinal portion from the rest, thus throwing the urogenital ducts into connection with a wide ventral part ot the lower aperture, urogenital sinus, while the intestine is left in communication with the narrower dorsal section. The anus, strictly so called, now appears as the opening of the alimentary canal, and in front of it the urogenital aperture forms a narrow vertical slit wider behind than before, and leading into the urogenital sinus.
In front of the last-named aperture there now rises a well-marked prominence of the integument, the rudiment of the still indifferent organ rei:)resenting the clitoris or penis. Into this jirominence the nrogenital groove runs forward, and surrounding the prominence in front, and continued downwards on each side of the urogenital opening, there is a raised ridge of integument, which is the foundation of the future lal)ia majora in the female, and of the two halves of the scrotum in the male.
The description of the later changes which occur in these parts in the development of fuller sexual differences will be given hereafter. Here it will be sufficient to state their general nature. In embryoes which are assuming the male type, the common eminence becomes gradually longer, more cylindrical and deeply grooved along its lower surface. The lateral ridges of the urogenital opening become united from behind forwards along the middle line, and this union is gradually continued into the ridges of the groove below the penis, so as to enclose a canal which becomes the urethra with its tegumental and spongy vascular coverings, and to form below this the scrotum, in which the raphe is the remains of the median union of the integmnent.
In female embryos, on the other hand, the cylindrical eminence remains comparatively small, and the groove along its lower surface ■widens into two folds, forming the laljicc minorcc or nymphae ; while the larger lateral integumental folds, retaining their prominence and remaining separate, constitute the labia majora. The groove is not closed, but widened and shortened so as to become the vulva, while more deeply the sinus urogenitalis shortens itself considerably so as to form the limited atrium vagiiuc, into which open the urethra from the urinary bladder and the now united lower portion of Midler's ducts forming the yagina.
From the previous statement, it appears that both the urinary and the reproductive organs take their origin in symmetrical pairs from the intermediate cell-masses of the mesoblast, which are situated to the outside at first, and subsequently below, the protovertebral columns. The earliest formed of these organs are the Wolffian bodies, by which the others are all intimately connected together in their development, so as, to form one great system. It further appears that, while the urinary organs are developed in an entirely similar manner in all embryoes, there are in the sexual organs certain departures from the common type b}^ which the peculiarities of the male and female are established. The general plan of development of these organs having been previously described, the history of the process will now be completed by an account of the further changes which they undergo.
FURTHER HISTORY OF THE3 DEVELOPMENT OF THE UROaENITAL
ORGANS.
===The Kidneys and their Ducts===
These organs are developed together from a mass of formative cells situated posteriorly on the dorsal aspect of the Wolffian bodies, their first hollows being formed as diverticula from the Wolffian duct.
The formative blastema of the kidney, as observed 133- Eatlike in the foetal calf, soon contams a series of club-shaped bodies v^'hich have their larger ends free and turned outwards, and their smaller ends or pedicles directed inwards towards the futiire hilus, where they are blended together. As the organ grows these bodies increase in number, and finally, becoming hollow, form the uriniferous tuhes. At fii-st, short, wide, and dilated at their extremities, the tubuli soon become elongated, narrow, and flexuous, occupying the whole mass of the kidney, which then appears to consist of cortical substance only. At a subsequent period, the tubuli nearest the hilus become straighter. and thus fomi the medullary substance. The tubuli, as sho-wTi by Valentin, are absolutely, as 'u-ell as relatively, wider in the early stages of formation of the kidney. The Malpighian corpuscles have been seen by Ratlike in a sheep's emin-yo, the kidneys of which measured only two and a half lines in length. Koliiker observed the kidneys already foi-med in the human embryo of between six and seven weeks, the ureter being hollow, and communicating with dilated cavities within the rest of the blastema. At eight weeks they had assumed their characteristic reniform shape, and about the tenth week they are distinctly lobulated. The separate lobules, generally about fifteen in number, gi-adiially coalesce in the manner already described ; but at birth, indications of the original lobulated condition of the kidney are still visible on the surface, and the entire organ is more globular in its general figui-e than in the adult. The kidneys are then also situated lower do-mi than in after-life.
In the advanced fcetus and in the new-born infant, the kidneys are relatively larger than in the adult, the weight of both glands, compared with that of the body, being, according to Meckel, about one to eighty at bu-th.
===The Suprarenal Bodies===
These organs have their origin in a mass of blastema, placed in front of and between the kidneys and the Wolffian bodies. They appear to originate in a single mass, and afterwards to become divided. Koliiker has also observed them in close connection with the substance in which the large sympathetic plexus of the abdomen is produced, but it is not ascertained that they have a common origin.
In the human emlnyo the suprarenal bodies are at the seventh or eighth week larger than the kidneys, and quite conceal them, but after that time their relative size diminishes, so that at about the tenth or twelfth week they are smaller than the kidneys. At six months, according to Meckel, the proportion of the suprarenal bodies to the kidneys is as 2 to 5 ; at birth the proportion between them is 1 to 3, whilst in the adult it is about 1 to 22. They diminish much in aged persons, and are sometimes scarcely to be recognised.
===The Urinary Bladder and Urachus===
It has elsewhere been stated that in the human eniljiTO the vesicular part of the allantois extending beyond the umbilicus is closed at a very early period. Its pedicle, however, remains in communication with the urogenital sinus, and receives the ureters from the developing kidneys. The lower part of the pe'dicle undergoes a gradual dilatation to form the urinary hladder, while at the connection of this part with the urogenital sinus a constriction occurs in the part which gives rise to the urethra. Tliis in the female opens at once into the original urogenital sinus, but in the male the passage is continued onwards through the penis by the median union of the parts below that organ.
The part of the allantois situated above or in front of the bladder within the abdomen remains very much narrowed as the urachus, a tapering process of the upper extremity of the bladder into which at first the internal cavity is prolonged, but which later consists only of the muscular and fibrous coats. This process may for a time be traced for a short distance within the umbilical cord, but at an early period all vestiges of its farther prolongation disappear.
Genital Cord; — In both sexes, as was first fully shown by Tiersch and Leuckart in 1852, the two Wolffian ducts become united by surrounding substances into one cord behind the lower part of the urinary bladder ; but retaining internally their separate passages until they reach the sinus urogenitalis. With this cord the Miillerian ducts are incorporated posteriorly, so that at one time there are four passages through the whole of the genital cord. The Miillerian ducts next coalesce into one at some little distance from their lower ends, and this fusion, progressing upwards and downwards for a considerable space, a single median cavity is produced which lies between the still separate canals of the Wolffian ducts. A large accumulation of tissue in its walls gives to the genital cord great thickness as compared with the neighbouring parts of the ducts where they emerge from its enclosure. The lower ]3art of the united Miillerian ducts thus comes afterwards to form the foundation of the vagina and lower part of the uterus in the female, and the corresponding prostatic vesicle with its occasional accompaniments, or the uterus masculinus of the male.
Pig. 608. — Transverse Sections of the Genital Cord in a Female Calf Embryo. Magnified 14 diameters (from Kolliker).
1, near the upper end ; 2 and 3, near the middle ; 4, at the lower end ; a, anterior, p, posterior aspect ; m, Miillerian ducts, united or separate ; W, Wolffian ducts.
REPRODUCTIVE ORGANS.
In the farther history of the development of the genital organs it will be expedient to consider them in the two sexes in succession under
Fig. 609. — Internal Genital Organs op a Male Human Embryo of S^ inches long (from Waldeyer).
t, body of the testicle with seminal canals formed ; c, epididymis, or upper part of Wolffian body ; w, Wolffian body, lower part, 1>ecoming paradidymis or organ of Giraldes ; w', Wolffian duct, becoming vas deferens ; ff, gubernaculum.
the three heads of 1st, the productive organs ; 2nd, the conducting passages ; and 3rd, the external organs.
===Reproductive Glands===
It has already been explained that although the male and female productive organs lake their origin fi'om a mass of blastema which is on the whole identical in the two sexes, yet there are such differences in the development ol' the essential parts of the respective structures of the ovary and testicle as almost to warrant the conclusion that these organs are from the firsfc in some measure distinct.
The distinction of sex begins to be perceptible in the internal organs of the human eminyo in the seventh week, and becomes more apparent in the eighth. The reproductive gland is from the first connected with the Wolffian body, of which its blastema seems to be actually a part ; and it remains attached to it, or after its disappearance to the structure whichoccupies its place, by a fold of the peritoneal membrane, constituting the mesorchiura or mesovarium. Upper and lower bands fix the Wolffian body ; the upper passing to the diaphragm may be named the diaphragmatic ; the lower running down towards the groin from the Wolffian duct, contains muscular fibres and constitutes the future gubemaculum testis and round ligament of the uterus.
===The Testicle===
In male embryoes at the tenth week already seminal canals are visible, being at first, according to Kolliker, entirely composed of cells, but by the eleventh and twelfth weeks the tubes have become somewhat smaller, longer, and are now branched and possess a membrana propria. There is also by the end of the third month a commencement of lobular division, and the body of the testis is now covered with a condensed laj-er of fibrous tissue which forms the tunica albuginea.
In connection with the development of the spermatic filaments or spennatozoa, the essential part of the male reproductive element, previously referred to at p. 448 of this volume, it may here fui'ther be stated that renewed researches by Neumann (Ai'chiv filr Microsc. Anat., vol. xi., p. 292), appear to show that the doubts thrown by Sertoli and Merckel on the statements of V. Ebner are not well founded, that there really exist within the seminal ducts protoplasmic columns stretching from within the wall of the tube into its cavity, and that the spennatic filaments are produced in connection with the inner ends of the columns as branched lobes, amounting- in general to ten or twelve in number, in which the heads lie outwards imbedded in the protoplasmic stalk, and the filaments or tails are directed inwards towards the central lumen of the tube. Each stalk, or sjjcrmatohlant, as Neumann proposes to name it, possesses a large clear nucleus with nucleolus, and previous to the formation of the heads there are nuclei corresponding in number to them, which do not, however, appear to arise directly from division of the main nucleus of the stalk, but rather to be formed as free nuclei in the protoplasm. Each spermatozoon consists of three parts, which are most easily disting-uished in those which have not reached their stage of full development. These parts are, 1st, the head, or, as it may from its form in some animals be called, the hook ; 2nd, the body or middle pai-t, forming a slight thickening, and frequently of a vesicular appearance ; and 3rd, the filament or tail. The fii-st of these proceeds more immediately from a nucleus, the second is the remains of the protoplasmic covering of a spennatoblastic lobe, the feird is a ciliated production from the last. The bases of the spermatoblasts ai-e attached to the inner sm-face of the fibrous coat of the seminal canals, to which they furnish a complete lining, being set closely upon it like a layer of hexagonal plates. The stalks rise as tapering processes from these plates, and in the intervals between the stalks, necessarily largest towards the periphery, there is a number of opaque gi-anular spherical cells, the exact nature of which is not ascertained, but which it is conjectured may be the source of new spermatoblasts.
An interesting view is presented by Neumann of the analogy of these spennatoblasts of the seminal tubes with the much elongated ciliated cells whichare found in the canals of the coni vasculosi and tube of the epididymis, in accordance with which it may be held that the spermatic filaments are a peculiar forai of ciliary structm-e, developed from protoplasmic elements of a cellular nature, but which undergo a peculiar modification in connection with the special destination. cf the spermatozoa.
===The Ovary===
Considered as a glandular organ the ovary differs from other glands by the absence from it of excretory ducts, and by the
Fig. 610. — Internal Okgans of a Female human foetus of 3.| INCHES LONG. MAGNIFIED (from Waldeyer).
o, the ovai7 full of primordial ova ; e, tubes of the upper part of the WoMan body forming the epoophoron (parovarium of Kobelt) ; \V, the lower part of the Wolffian body forming the paroophoron of His and Waldeyer ; W', the Wolffian /'- .C"f ' 1 duct; M, the Miillerian duct; m, its upper fimbriated opening separation of its conducting passages from the glandular or productive part of its structure. Like the testicle it begins to manifest its peculiar characteristics by the seventh or eighth week, when the germ-epithelium has attained
considerable thickness, and forms a decided prominence on the mesial side of the Wolffian body. The farther development of the glandular part of the organ consists mainly in the formation of ovigerms and ova, and the implantation of these in Graafian follicles by a peculiar combination or intermixture of the superficial germinal cells with the deeper blastema which forms the stroma of the organ.
In a former part of this volume, imder Ovary, p. 478, the development of the primordial ova from a certain number cf the cells of the germ-epithelium and their enclosure in Graafian follicles by the growing stroma of the ovary have been described according to the most recent obsen'ations of "Waldeyer, Kolliker and J. Foulis. The publication of the very careful researches of the last observer enables us to add some important details to the previous description.
Figure 611, copied from some of Foulis's plates (Trans. Roy. Soc, Edin., 1875) will best show what from these observations appears to be the most j^robable view of the mode of development lof ova in the human ovary. At e, fig. 611. B, is seen a portion of the germ-epithelium, and at c', one of the cells undergoing enlargement and conversion into an ovigerm or primordial ovum. Of this the outer jirotoplasm becomes the yolk, and the nucleus the germinal vesicle with its nucleolus or macula. At o, a single o'S'igerm, and at o\ clusters of ovigerms in various stages of development have sunk into the ovarian stroma, and are beingsurrounded collectively and individually by the growth of the connective tissue of the ovarian stroma advancmg from below. Some of the o^^germs in the clusters are more advanced than the rest, and in these, as also in the isolated ovigerm represented in C, a covering of altered connective tissue coi-puscles is seen to be forming round the yolk protoplasm. This is the oi-igin of the cells of the tunica granulosa, which Foulis has shown are not produced, as W^aldeyer believed, from germ-epithelial cells, but from the interstitial connective tissue of the deeper ovarian stroma. In A, o, o, the cell fibres of the stroma («, «,) are seen suiTOunding several individual ova, so as to furnish the first elements of the wall of the Graafian follicles enveloping the ova, and covering immediately the granular cells. In D, representing an ovum somewhat farther advanced, the enlarged yolk-protoplasm and the geiininal vesicle are shown entire, with a fragment of the granular cell covering and fibro-cellular wall of the Graafian follicle ; but the zona pellucida is not yet perceptible.
The further steps in the formation of the ovum, as ascertained by the observations of Foulis, consist mainly in the enlargement of the mass of yolk protoplasm, the formation of a certain quantity of albuminous and fatty granules in combination with it (deutoplasm of Edw. van Beneden) ; and the formation externally of the zona pellucida or yolk-membrane by a consolidation cf the outer layer of the yolk substance. And here it may be remarked that the recent observations of Oellacher and Balfour on the radiated structure of the yolk protoplasm may explain in some degree, or be connected with the linear radiated marking of the zona pellucida.
Fig. 611. — Views of the Formation op Ova and Graafian Follicles in the Ovart
(from Foulis). A, small portion of the ovary of a human fcetus of SJ montbs, showing primordial ova imbedded in the stroma ; o, larger primordial ova ; o cluster of earlier ova ; n, fusiform corpuscles of the stroma. B, portion of the ovary near the surface in a human fcetus of 7 A months, showing the manner of inclusion of the germ epithelium corpuscles in groups in the ovarian stroma ; e, germ epithelium ; e', one of the cells enlarging into a primordial ovum before sinking into the stroma ; o, a larger cell imbedded, becoming an ovum ; o', groups of ovigerms or germ cells which have been surrounded by the stroma. C, young ovum from the same ovaiy, isolated ; p, yolk protoplasm. D, ovum more advanced, enclosed in condensed stroma, whichbegins to form a Graafian follicle ; p, yolk protoplasm ; V, germinal vesicle with macula ; g, the fusiform corpuscles now converted into the granular cells ; Gf, condensed stroma forming the wall of the Graafian follicle.
Such is the number of ova formed in the manner now described, that in the human foetus of six to seven months the whole substanc-e appears to consist of them and their newly formed Graafian follicles, by which each primordial ovum is closely embraced. A uniform layer of such ova of nearly equal size is especially to be found tovs^ards the surface ; but in the two later months of foetal life some of the ova and follicles advance to a farther stage of development, and increase in size, and this advance is invariably accompanied by a change of position of these ova to a deeper stratum of the ovary. The most advanced of the ova, therefore, are situated deepest in this the earlier stages of the ovarian development. It is different, however, when some "years after Ijirth, and still more towards the age of puberty, a few of the Graafian follicles expand to a great extent, and ultimately when mature reach the diameter of about a quarter of an inch, for then the expanding Graafian follicle gradually approaches the surface of the ovary, or perhaps rather, during the rapid expansion of the follicle, the ovarian stroma gives way by absorption between the follicle and the surface.
As the Graafian follicle expands with the slightly enlarging ovum, the thickness of the layers of condensed connective tissue or stroma round the ovum increases, and thus there are gradually formed the layers which liave been described as the follicular walls, while blood-vessels penetrate into them so as to form the vascular network of the covering. Within the follicle the granular cells multiply so as to form several layers lining the •whole follicle and closely covering the ovum. As yet there is no space between the ovum and wall of the follicle except that which is occupied by the granular cells, and for a long time the follicle is not larger than to enable it to enclose the ovum ; but in the more advanced stages a proportionally great enlargement of the follicle takes place, in consequence of the separation of two layers of the granular cells, so as to form a space in which fluid accumulates, and thus one or more layers •of cells are left lining the expanded follicle and constituting its tunica granulosa, while those covering the ovum, which is now thrown to one side of the follicle, form the investment known as the discus proligerus, -which appears as a reflected portion of the tunica granulosa (see figs. 335 and 336, p'3. 473 and 475).
As connected with the difference in the seat and mode of development of the ■essential parts of the male and female productive organs, the important question presents itself of the possibility or reality of the simultaneous coexistence in any cases of malformation of ovaries and testes on one or both sides of the body in the same individual. From what has been stated above, the possibility of such coexistence may perhaps be theoretically admitted. On this subject the reader may consult an interesting account by Dr. C. L. Heppner of St. Petersburg (Reichert's and Dubois Reymond's Ax-chiv for 1870, p. 679), of a hermaphroditic child which lived two months after biiiih, in which, along with a considerable amount of the better kno-mi conditions of approximation or mingling of the sexual charapters, it appeared that two organs coexisted, in one of which, agreeing in all respects with the ovary, primordial ova in Graafian folUcles were observed, and in another of a distinctly rounded iorm and compact structm'e, and so far corresponding to the testicle and unlike any of the other known vestigial organs, branched and coiled tubes, filled with cells in a manner exactly the same as those of the seminal canals, were ascertained by microscopic observation to exist. The jiarovarium (epididymis or coni vasculosi) also existed.
===The genital passages===
The existence of two sets of tubes between the iuteinal productive organs and the external parts has already been adverted to as a feature common to both sexes. The female organs contrast Avith the male in the large development of one of these tubes, viz.. the Miallerian ducts into their passages, and in the abortive disappearance of the greater part of the Wolffian ducts ; while in the male the ducts of Miiller suffer in a great measure the abortive retrogradation, and the seminal conducting tubes are produced out of canals formed within special parts of the Wolffian body and the whole of the Wolffian duct. But as in all embryoes of whatever sex both sets of tubes are originally present, while a different one of the original tubes becomes developed into the respective permanent conducting passages, vestiges of the other original tubes are invariably present in various degrees in both sexes.
The Female passages. — In the female, the vagina, uterus, and Fallopian tubes are formed out of the Miillerian ducts. That portion of the ducts in which they become fused together is developed into the vagina, the cervix, and part of the body of the uterus ; and the pecu
Fig. 612. GKAJI OF THE FEMALE Type op Sexual Organs.
This and figure 615 represent diagrammatically a state of the parts not actually visible at cue time ; but they are intended to illustrate the general type in the two sexes, and more particularly the relation of the two conducting tubes to the develop inent of one as the natural passage in either sex, and to the natural occurrence of vestiges of the other tube, as well as to the persistence of the whole or parts of both tubes in occasional instances of hermaphroditic nature.
1, the left kidney ; 2, suprarenal body ; 3, ureter, of which a i)art is removed to show the
parts passing within it ; 4, urinary bladder ; 5, urachus ; o, the left ovary nearly in the place of its original formation ; p o, parovariiun, ejioophoron of Waldeyer ; W, scattered remains of Wolffian tubes near it, parooi^horon of Waldeyer ; d G, remains of the left Wolffian duct, such as give rise to the duct of Gaertner, represented by dotted lines ; that of the right side cut short is marked w ; /, the abdominal opening of the left Fallopian tube ; u, the upper part of the body of the uterus, presenting a slight appearance of division into cornua ; the Fallopian tube of the right side cut short is marked in ; g, round ligament, corresponding to gubernaculum ; i, lower part of the intestine ; V a, vagina ; 7i, situation of the hymen ; C, gland of Bartholin (Cowper's gland), and immediately above it the urethra ; c c, corpus cavernosum clitoridis ; s c, vascular bulb or corpus spongiosum ; n, nympha ; I, labium ; v, vulva.
liaritv of the mode of fusion accounts for the occurrence, as a rare anomaly, not only of double uterus, but of duplicity of the vagina, coincident with communication between two lateral halves of the uterus. The next following part of the Miillerian duct, constitutes in animals with horned uteri, the cornu of the uterus ; but in the human subject it remains comparatively short, entering into the formation of the upper part of the organ. The remaining upper portion of the Miillerian duct constitutes the Fallopian tube — becoming at first open and subsequently frino-ed at a short distance from its upper extremity.
The pediculated hydatid of the fimbriated extremity (Hydatid of Morgagni) appears to be the remains of the original upper end of the Miillerian tube. The additional or accessory fimbrise and openings referred to at p. 471, and by Henle in his Handbuch, vol. ii., p. 470, may admit of explanation on the supposition of the duct of Miiller having remained open at these places.
In the human embryo of the third month the uterus is two-homed, and it is by a subsequent median fusion and consolidation that the triangular body of the entire organ is produced. The comua uteri, therefore, of the human uterus correspond with the separate comua of the divided uterus in animals, and this explains the occasional malformation consisting in the gi-eater or less division of the uterine cavity and vagina into two passages. There is no distinction in the human foetus in the third and fourth month between the vagina and uterus. In the fifth and sixth months the os uteri begins to be formed, and the neck is subsequently gradually distinguished. Thickening succeeds in the walls of the uterine portion ; but this takes place first in the cervix, which up to the time of birth is much larger and thicker than the body of the uterus (KoLLiker).
Fig. 613.— Female Genital Okgans of the Embryo with the Remains of the Wolffian Bodies (after J. Miiller).
A, fi'om a foetal sheep ; n, the kidneys ; h, the ureters ; c, the ovaries ; d, remains of ■Wolffian bodies ; c, Fallopian tubes ; /, their abdominal openings ; g, their union in the body of the uterus. B, more advanced from a foetal deer ; a, body of the uterus ; b, comua ; c, tubes ; d, ovaries ; e, remains of Wolffian bodies. C, still more advanced from the hviman fcetus of three months ; a, the body of the uterus ; b, the round ligament ; c, the Fallopian tubes ; d, the ovaries ; e, remains of the Wolffian bodies.
In the meantime the Wolfiian bodies undergo a partial atrophy, and their ducts become more or less obliterated and abortive in different parts. The most constant vestige of the "Wolffian bodies in the female is the now well-known body of Rosenmiiller or Parovarium of Kobelt (Eosenmiiller, Quoidam de Ovariis Embry. Human., Lipsiaj. 1802 ; Kobelt. der Nebeneierstock des Weibes, Heidelberg-, 1847), which has already been described at p. 480 of this volume, the ciHwj)horon of Waldeyer, and which, being produced out of the same elements as the epididymis of the male, presents a remarkable resemblance to that body. The canal uniting the radiating tubes (coni vasculosi) of this organ is also usually persistent, but ceases at a short distance below. In the sow and several ruminants, however, the subdivided upper tubular part or epoophoron has disappeared, and the main tube (middle part of the Wolffian duct) remains in the (hu-t of Gaertner, a strong, slightly undulated tube, which is traceable, first free in the broad ligament of the uterus, and lower down becoming incorporated with the wall of the uterus and vagina, upon which last it is lost.
Fig. 614. — Adult OvARr, Parovarium anu FalluI'Iaii Tube (from Farre, after Kobelt).
a, a, Epoophoron (parovarium) formed from the xipper part of the Wolffian body ; b, remains of the uppermost tubes sometimes forming hydatids ; c, middle set of tubes ; d, some lower ati-ophied tubes ; c, atrophied remains of the Wolffian duct ; /, the terminal bulb or hydatid ; h, the Fallopian tube, originally the duct of Midler ; i, hydatid attached to the extremity ; I, the ovary.
===The Male Passages===
The conversion of the Wolffian duct into the vas deferens of the testicle was first demonstrated in animals by Ratlike, in correction of the views of J. Miiller (Meckel's Archiv, 1833), and was further proved and illustrated by H. Meckel and Bidder (H. Meckel, Zur Morphol. der Ham uud Geschlechts-Organe der Wirbelthiere, Halle, 1848 ; Bidder, Male Organs in the Amphibia, Dorpat, 184G). KuUiker showed that a similar process occurs in the human embryo, and that a communication established between the seminal tubes of the testicle (rete testis) and some of the upper tubes of the Wolffian body gave rise to the epididymis.
The observations of Cleland and Banks first pointed out clearly the difference between the structure of the upper nonglomerular, or simple tubular part of the Wolffian body, and that of the lov.er and glomerular, or primordial-kidney part.
In the male, the Miillerian ducts are destined to undergo little development and are of no physiological importance, while the ducts of the Wolffian Iwdies, and probably also some part of their glandular substance, form the principal part of the excretory apparatus of the testicle. The rmited portion of the Miillerian ducts remauis as the vesicula prostatica, which accordingly not only corresponds with the uterus, as was shown by Weber, but likewise, as pointed out by Leuckai-t. contains as much of the vagina as is represented in the male. In some animals the vesicula prostatica is prolonged into comua and tubes ; but in the human subject the whole of the ununited parts of the Miillerian ducts disappear, excepting, as suggested by Kobelt. their upper extremities, which seem to be the source of the hydatids of Morgagni. The excretory duct of the Wolffian body, from the base of that body to its orifice, is converted into vas deferens and ejaculatory duct, the vesicula seminalis being formed as a diverticulum from its lower part (Waldeyer).
With respect to the fomiation of the epididymis, it appears certain that the larger convoluted seminal tube, which foi-ms the body and globus minor of the epididymis, arises by a change or adaptation of that part of the Wolffian duct which runs along the outer side of the organ. The vas aben-ans or vasa aberrantia of Haller appear to be the remains also, in a more highly convoluted foi-m, of one or more of the tubes of the Wolffian body still adhering to the excretory duct of the organ, and their communication with the mam tube of the epididymis receives an explanation from that circumstance. As to the coni vasculosi in the upper part of the epididymis, it has been customary to regard them as produced by a transformation of the tubes and duct in the upper part of the Wolffian body, according to the views most fully given by Kobelt ; but, according to the more recent observations of Banks, the origin of the coni vasculosi is most jn'obably due to a process of development occm-ring in a new stnictiure or mass of blastema which had been jireviously observed by Cleland, and which is foiTued in connection with the upper end of the "Wolffian body, and close to the Miillerian duct. "Within this blastema Cleland showed that the tubes of the efferent seminal vessels and the coni vasculosi, together with the tube which connects them, are formed anew, while the tubes of the lower primordial -kidney part of the "Wolffian body are undergoing an atroi^hic degeneration. This has been confirmed by the detailed observations of Banks, who has further shown the continuity of their uniting tube with the "\Yolffian excretory duct.
Fig. 615. — Diagram of THE Male Type of Sexual Organs.
1, 2, 3, 4, and 5, as in iigure 612 ; t, testicle in the place of its original formation ; e, caput eiiididymis ; v d, vas deferens ; W, scattered remains of the Wolffian body, constituting the organ of Girakles, or the paradidymis of Waldeyer ;
V h, vas aberraus ; on, Miillerian duct, the upper part of -which remains as the hydatid of Morgagni, the lower part, represented by a dotted line descending to the prostatic vesicle, constitutes the cornu and tube of the iiterus masculinus ; g, the gubernaciilum ;
V s, the vesicula seminalis ; p r, the prostate gland ; C, CowiJer's gland of one side ; c f, corpora cavernosa penis cut sliort ; s p, corpus spongiosum urethraj ; s, scrotum ; t' , together with the dotted lines above, indicates the - direction in Avhich the testicle and epididymis change place in their descent from the abdomen into the scrotum.
According to this view, the caput epididymis must be regarded, not simply as a conversion of the ujiper part of the "Wolffian body, but rather as a new formation, or superinduced development of tubes in blastema connected with it.
The coni vasculosi, so fonned, become connected with the body of the testicle by means of a short straight cord, which is afterwards subdivided into the vasa efferentia. The peritoneal elevation descending from the testis towards the lower extremity of the "Wolffian body, is the upper part of the plica gubernatrix, and becomes shortened as the testicle descends to meet the lower end of the epididjTiiis ; the peritoneal elevation which passes do'OTi into the scrotum, and is continuous with the other, is the more important part of the plica gubernatrix, connected with the gnbernactilum testis. The spennatic arteiy is originally a branch of one of those which go to the "Wolffian body, and ascend from the surface of the Wolffian body to the upper part of the testis, along the ligaments connecting them ; but, as the testis descends, the artery lies entnely above it, and the secreting substance of the Wolffian body remains adherent to it ; and hence it is that the organ of Gii-aldes, which consists of persistent "\\'olffian tubules, is found in a position superior to the ei^ididymis. (For a fuller account of this subject the reader is referred to Banks "-On the Wolffian Bodies," Edin 18G-i.)
Fig. 616. YiEW FROM BEFORE OF THE Adttlt Testis and EpididtMis (from Farre, after Kobelt).
a, a, convoluted tubes in ■ the head of the epididymis developed from the upper part of the Wolffian body ; b and /, hydatids in the head of the epididymis ; c, coni vasctdosi ; (/, va.sa aberrantia ; /(, remains of the duct of ]\Udler ■with i, the hydatid of IMorgagni at its upper end ; , body of the testis.
===The Descent of the Testicles===
The testicles, which are originally sitixated in the abdominal cavity, pass down into the scrotum before birth. The testicle enters the internal inguinal ring in the seventh month of foetal life : by the end of the eighth month it has usually descended into the scrotum, and, a little time before birth, the naiTow neck of the peritoneal pouch, by which it previously communicated with the general pei-itoneal cavity, becomes closed, and the process of peritoneum, now entu-ely shut off from the abdominal cavity, remains as an independent serous sac. The peritoneal pouch, or processus vaginaliB, which, passes do-mi into the scrotum, precedes the testis by some time in its descent, and into its posterior part there projects a considerable columnar elevation already alluded to, which is filled with soft tissue, and is termed 2>lica (juhcrnatrix . There is likewise a fibrous structui'e attached inferiorly to the lower part of the scrotum, and surrounding the peritoneal pouch above, which may be distinguished as the (jul}t'rnacular cord, both this and the plica gubernatrix being included in the general tei-m g uhernaciiluvi testis (J. Hunter). The gubernacular cord consists of fibres which pass downwards from the sub-peritoneal fascia, others which pass upwards from the superficial fascia and integmnent, and others again which pass both upwards and downwards from the internal oblique muscle and the aponeurosis of the external oblique ; it exhibits, therefore, a fusion of the layers of the abdominal wall. Superiorly, it surrounds the processus vaginalis, without penetrating the plica gubernatrix ; and the processus vaginalis, as it grows, pushes its way down through the gubernacular cord and disperses its fibres. By the time that the testis enters the internal abdominal ring, the processus vaginalis has reached a considerable way into the scrotum ; and. as the testis follows, the plica gubernatrix becomes shoiler, till it at last disappears ; but it cannot be said that the shortening of the plica is the cause of the descent of the testicle, and much less that (as has been held by some) the muscular fibres of the gubernacular cord are the agents which effect this change of position. The arched fibres of the cremaster muscle make their appearance on the surface of the processus vaginalis as it descends, while its other fibres are those which descend in the gubernacular cord. (See, for a further account of this process, and the various views which have been held with regard to the descent of the testicles, Cleland, " Mechanism of the Gubemaculum Testis." Edinburgh, IS.JG.)
===The External Organs===
In the human embryo, as in that of animals, the external organs are up to a certain time entirely of the same form in both sexes ; and the several organs which aftenvards distinguish the male and female externally take their origin respectively from common masses of blastema of precisely similar structure and connections. The common cloaca exists till after the fifth week, and the genital emmence from which the clitoris or penis is formed makes its appearance in the course of the fifth and sixth weeks in front of and within the common orifice. In the course of the seventh and eighth weeks the common orifice is seen to become divided into two parts, viz., the longer slit of the genito-urinary apeiture anteriorly, and the naiTower and more rounded anal aperture posteriorly : but the exact manner in which the separation of these two apertures takes place has not yet been acciu'ately traced. It is intimately connected with the formation of the urogenital cord as an independent stmcture, and is probably mainly effected by the advance from the sides and posteriorly of septal bands which separate the lower pai"t of the intestine. Somewhat later, or in the ninth and tenth weeks, a transverse integumental band completes the division between the anal and the urogenital orifices, which band forms the whole of the so-called perineum of the female, and the part of the perineal integument in the male which is situated behind the scrotum ; the raphe being most obvious in the male sex.
The cutaneous folds, or cii-cular genital ridge, which are afterwards converted into mons Veneris, labia majora, and scrotum, as well as the lips of the urogenital furrow, which are converted into the nymphte of the female and unite as integument below the penis in the male, are both of early formation and at first precisely the same in all embryoes. In this condition, which continues until the eleventh or twelfth week, the parts appear alike in both sexes, and resemble very much the more advanced female organs. The rudiments of JJartholui's or Ceirpcrs glands are, it is said, seen at an early period, near the root of the rudimentary clitoris or penis, on each side of the genito-uininary passage.
In the female, the tvro lateral cutaneous folds enlarge, so as to cover the clitoris and form the labia majora. The clitoris itself remains relatively smaller, and the gToove on its under surface less and less marked, owing to the opening out, and subsequent extension backwards, of its margins to form the ntjinplKP. The vascular bulbs remain distinct and separate, except at one point where they run together in the glans clitoridis. The hijmcn begins to appear about the fifth month as a fold of the lining membrane at the opening of the genital passage into the urogenital sinus. Within the vestibule, which is the shortened but ■widened remains of the urogenital sinus, the urethral orifice is seen, the lu'ethra itself undergoing considerable elongation.
In the male, on the contrary, the j;c'«w continues to enlarge, and the margins of the groove along its under surface gradually unite from the primitive urethral orifice behind, as far forwards as the glans, so as to comiilete the long canal of the male itrcthra, which is therefore a prolongation of the urogenital sinus. This is accomplished about the fifteenth week. "When this union remains incomplete, the abnormal condition named iLUpo.^padlas is produced. In the meantime the prcjniec is formed, and, moreover, the lateral cutaneous folds also unite from behind forwards, along the middle line or raphe, and thus complete the scrotum, into which the testicles descend in the course of the eighth month of fojtal life.
The corpora cavernosa, which are at first separate, become united in their distal portions in botli sexes ; but the corpus spongiosum lu'ethraj which is also originally divided in all embryoes, and in the female remains so in the greater part of its extent, becomes enlarged in the male in the glans penis, and its two parts united mesially both above and below the urethra, so as to enclose the whole of that tube from the bulb forwards to the glans.




Revision as of 18:39, 11 October 2012


DEVELOPMENT OF THE BLOOD-VESSELS

The Principal Arteries. The Aorta

The most interesting part of this history is that relating to the development of the aorta and the larger vessels arising from it. The double condition of the main trunk of "the aorta has already been referred to as existing in the chick up to near the end of the second day. About the fortieth hour the inedian fusion or coalescence of the two vessels begins to take place in the dorsal region, by their external union, at first in a very limited space, and very soon afterwards by the formation of a perforation through their united walls. The union of the two vessels which begins in the dorsal region extends itself backwards towards the lumbar vertebrae, and when it reaches the place where the omphalo-mesenteric arteries pass out on each side, these vessels, each of which was originally the continuation merely of one of the aortas, appear now as branches of a single and median aorta. The iliac vessels are the next large vessels formed from the hinder part of the aorta. The first vessels belonging to these trunks are not, however, those of the lower limbs, for these are not yet formed ; but the umbilical or hypogastric arteries, developed at a very early period in connection with the allantois, and subsequently attaining to a large size along with the growth of the placenta. As the limbs are formed, arteries are developed in them, and these are branches of the main aorta ; but they are for a long time comparatively small, w'hile the umbilical arteries speedily attain a large size, so that, even up to the conclusion of foetal life, they appear to form the principal part of the two large vessels into which the aorta divides at its lower extremity. The middle sacral artery may be looked upon as the continuation of the median stem of the aorta, and probably originates from a double vessel in the same manner as the aorta itself.


Fig. 591. — Transverse Section through the Dorsal Region op an Embryo-Chick OP THE Second Day (from Foster and Balfour, after His). M, medullary canal ; Pv, proto -vertebral column ; w, rudiment of Wolffian duct in the intermediate mass; Ch, notocliord ; Ao, one of the two aortas ; A, epiblast ; C, hypoblast ; BC, splanchnopleure ; Pp, pleuroperitoneal space.


Fig. 592.- — Transverse section through the Dorsal region op an Embryo Chick, END op Third Day (from Foster and Balfour).

Am, amnion ; m p, muscle plate ; CV, cardinal vein; Ao, dorsal aorta at the point where its two roots begin to join ; Ch, notochord (the line does not quite reach it) ; Wd, Wolffian duct; Wb, commencement of formation of Wolffian body ; ep, epiblast ; so, somatopleure ; Sp, splanchnopleure ; hy, hypoblast. The section passes through the place where the alimentary canal {hy) communicates with the yolk-sac.



The double state of the main aorta when first formed in the foetus was discovered by Serres, and described bj him in his 4tli Memoir on Transcendental Anatomy (Annal. des Scien. Nat., 18130), but was doubted by Von Baer, as Serres's observations did not show the relation of the primitive trunks of the aorta to the pharyngeal vascular arches. The fact of the original double condition was, however, placed beyond doubt by Allen Thomson (Edin. New Philos. Journal, ISoO) by the method of tranverse sections, then fii-st employed as a means of embryological investigation, and the process of median union was traced in full detail. The relation of this process to the occurrence of a permanent double canal in the aorta as a malformation, as described by Vrolik. Schroder van der Kolk and Cruveilhier. and obseiwed in at least one case by Allen Thomson, has already been referred to in vol. i., p. 350.

According to Serres, the vertebral arteries within the cranium are originally separate, and the basilar artery results from their mesial union or fusion in the same manner as occurs in the aorta, and the median union of the anterior cerebral arteries in the forepart of the Circle of Willis is another example of the same process. It seems probable that the internal cross band observed by John Davy in the interior of the basilar artery (Researches Physiol, and Anatom., lSo9, p. 301) may be a remains of the septum or united walls of the two vertebral arteries.

Aortic OX' Branchial Arches

The two primitive arterial arches which lead into the dorsal aorta from the arterial bulb of the rudimentary heart, at the time of the establishment of the first circulation, are the most anterior of a series of five pairs of vascular arches which are developed in succession round this part of the pharynx ; and which, since their discovery by Eatlike in 1S25 (Oken's Jsis, 1825) have been regarded with much interest, as corresponding with those vessels which are the seat of development of the subdivided blood-vessels of the gills in fishes and amphibia. These vascular arches thus exhibit in the amniota, along with the branchial or pharyngeal clefts and visceral plates, a typical resemblance to the structure of gills, although no full development of these respiratory organs occurs in such animals, but they furnish by their various transformations the basis of formation of the permanent pulmonary and aortic stems and the main vessels to which they give rise.

The form and position of the primitive aortic arches, up to the time of their transformation into permanent vessels, is nearly the same in reptiles, birds and mammals ; and the main differences in the seat and distribution of the large permanent vessels are to be traced to changes in the openness and extent of growth of the several arches. The five pairs Of arches do not all co-exist at the same time, for they are developed in succession from before backwards, and by the third day of incubation, or by the corresponding period of the fourth week in the human embryo, when the posterior arches have been formed, already a part of the anterior arches, beginning with the first one, has become obliterated. Each of the first four branchial arches occupies a place in the substance of the pharyngeal or visceral plates, and in front of one of the pharyngeal clefts. The first or anterior is therefore situated in the inferior maxillary plate, and in front of the tympano-Eustachian, or first pharyngeal cleft ; and the fifth arterial arch is placed behind the fourth pharyngeal cleft, and in the substance of the neck, in which there is no distinct bar or plate in the higher animals, but which is the seat of a developed branchial bar in some aquatic animals.

The vessels forming the arterial arches are given off on each side in succession from two short canals, into which the primitive arterial bulb divides immediately in front of the place where it joins the neck. These may be named the lower (ventral) or anterior aortic roots ; and similarly, when they have passed round the wall of the pharynx, the branchial arches unite in succession into a vessel on each side, thus forming the upper (dorsal) or posterior aortic roots.

On the third and fourth days in the chick, and from the fourth to the sixth week in the human embryo, there are still three complete pairs of arterial arches passing round the pharynx, and connected both before and behind with the anterior and posterior aortic roots previously mentioned. The transformations of these arches were in part traced by Von Baer and various other observers, but the fuller knowledge of their changes is due to the later researches of Eatlike (Mem. of 


Fig. 593. — Diagram of the Aortic or Branchial Vascular Arches of the Mammal, with their transformations giving rise to the permanent arterial Vessels (accordiug to Ilatlike, slightly altered).

A, Primitive arterial stem or aortic Lnlb, now divided into A, the ascending part of the aortic arch, and P, the pulmonary ; a, the right ; a', the left aortic root ; A', the descending aorta. On the right side, 1, 2, 3, 4, 5, indicate the five Ijranchial primitive arterial arches ; on the left side, I, II, III, IV, the four branchial clefts, which, for the sake of clearness, have been omitted on the right side. It will be observed, that while the fourth and fifth pairs of arches rise from the part of the aortic bulb or stem, which is at first undivided, the first, second, and third pairs are branches above c, of a secondary stem on each side. The permanent systemic vessels are represented in deep shade, the pulmonary arteries lighter ; the parts of the primitive arches, which have only a temporary existence, are drawn in outline only, c, placed between the permanent common carotid arteries ; ce, the external carotid arteries ; ci, c'l, the right and left internal carotid arteries ; s, the right subclavian rising from the right aortic root beyond the fifth arch ; r, the right vertebral from the same opposite the fourth arch ; v', s', the left vertebral and subclavian arteries rising together from the left or permanent aortic root opposite the fourth arch ; P, the pulmonary arteries rising together from the left' fifth arch ; d, the outer or back part of the left fifth arch, forming the ductus arteriosus ; j)n, 2^n , the right and left pneumogastric nerves, descending in front of the aortic arches, with their recurrent branches represented diagrammatically as passing behind, with a view to illustrate the relations of these nerves respectively to the right subclavian arteiy (4) and the arch of the aorta and ductus arteriosus {d).


Vienna Acad., 1857), and although some 'points are still left in doubt, their history may now be given from these observations, and the supplemental illustration derived from the investigation of the various examples of congenital malformation, the greater number of which are manifestly related to variations in the natural mode of transformation. This will be explained by reference to the diagram in fig. 593.


From these researches it appears that the permanent vessels owe their formation to the persiscence of certain of the foetal arches or parts of them, while other arches or portions of them become obliterated and disappear. Thus it is ascertained that in mammals the main aortic arch, which in the adult passes to the left of the trachea and gullet, is formed by the persistence of the fourth embryonic arterial arch of the left side, which not only remains patent, and becomes connected with the aortic stem of the arterial bulb, but keeps pace by its increased width and the development of its walls with the rate of growth in the other parts of the body, so that it soon surpasses all the rest of the arches in its width of calibre and thickness of its walls. In birds, however, the permanent aortic arch passes to the right of the trachea and gullet, and it is formed by the persistence of the fourth embryonic arch of the right side ; while, in all reptiles, as there are two permanent aortic arches, it is by the persistence of both the right and left foetal arches that the two aortas are produced, the right being that which is most directly connected with the systemic or left ventricle.


The pulmonary arteries of mammals would appear by Ratlike's observations to be developed in connection with only one foetal arterial arch, viz., the fifth of the left side, from the middle part of which they appear as branches, and the whole fifth arch of the right side undergoes rapid atrophy and ultimate obliteration. The first part of the left fifth arch, becoming the common pulmonary artery, is connected with that division of the arterial bulb which is separated as the pulmonary stem ; but the remote part of this arch also remains fully patent, and undergoing equally with the rest of it full development, continues to lead into the left root of the aorta as ductus arteriosus Botalli, which serves to convey the blood from the right ventricle of the foetal heart into the descending aorta, but becomes obliterated at the time of birth.


This duct is therefore in mammals due to a persistent condition of the fifth left branchial arch. But, in birds and reptiles, it appears that the process of transformation is somewhat different, for in them the right and left pulmonary arteries (excepting in those serpents in which there is .only one lung developed) are formed in connection with the respective right and left fifth branchial arches, and there are thus two ductus arteriosi during foetal life, the short one of the right side corresponding to that which is left in mammals, and the longer one of the left side passing round the pharynx into the left aortic root. Both of these arches are obliterated at the time of the exclusion of the bird from the eg^ ; but in some reptiles the ductus arteriosi remain permanently open during life.


The subclavian and vertebral arteries were shown by Ratlike to spring from the posterior aortic roots at a place between the junction of the fourth and fifth arches. In mammals, the vessels on the left side are from the first in direct connection Avith the aortic root at the place which they permanently occupy ; but upon the right side, as the fourth arch and the aortic root are obliterated posteriorly, the passage for blood from the aortic stem into the subclavian trunk is formed by the persistence of the forepart of the fourth right arch as far as the place where it meets the origin of the subclavian and vertebral arteries.


The common carotid trunks, occupying the region which afterwards becomes the neck, but which is at first absent or extremely short, are formed by the anterior divisions of the aortic roots ; while the external carotid artery is due to the persistence of a channel in the continuation of each anterior aortic root, and the internal carotid artery arises from the persistence of the crossing third arch and the upper part of the posterior aortic root.

Thus it falls out that, in man and a certain number of mammals, an innominate artery is formed on the right side by the union of the first part of the fourth right aortic arch leading into the right subclavian, and the right anterior aortic root which forms the common carotid ; while, on the left side, the carotid and subclavian vessels rise separately from the permanent aortic arch in consequence of the distance lying between them in the original foetal condition.

It does not come within the scope of this chapter to describe the further steps of development of these vessels, nor to enter into an explanation of the manner in which abnormal position of the arch of the aorta and its branches, or of the pulmonary arteries, may be supposed to arise. For further information on this subject the reader is referred to the short account of the varieties given in the description of the blood-vessels in the first volume of this work, as well as to the third volume of Henle's Handbuch, and to the special works of Tiedemann and Eichard Quain on the Arteries.


DEVELOPMENT OF THE GREAT VEINS

In the early embryo, before the development of the allantois, a right and a left omphalo-mesenteric vem bring- back the blood from the walls of the nmbilical vesicle, and unite to form a short trunk, the meatus venosus, which is continued into the auricular extremity of the rudimentary heart.

In the first commencement of the placental circulation, or in the fourth week of foetal life, two umbilical veins are seen coming from the placenta, and uniting to form a short trunk, which opens into the common omphalo-mesenteric vein. Very soon the right omphalo-mesenteric vein and right umbilical vein disappear. In connection with the common trunk of the umbilical and omphalo-mesenteric veins, two sets of vessels make their appearance in the yomig liver. Those furthest from the heart, named vena; Iwpatlca advehentcs, become the right and left divisions of the portal vein ; the others are the hepatic veins, vencv kcpaticce. Tcvclwnifs. The portion of vessel intervening between those two sets of veins forms the ductnn rcnoKiix, and the part above the hepatic vein, being subsequently joined by the ascending vena cava, forms the upper extremity of that vein. Into the remaining or left omphalo-mesenteric vein, open the mesenteric and splenic veins. The part above the latter forms the trank of the portal vein ; and the portion of vessel between the union of this with the umbilical vein and the origin of the venaj hepaticaj advehentes is so altered that the portal tiimk opens into the commencement of the right vena advehens.

At the time of the commencement of the placental cu-culation, two short transverse venous trunks, the ductii of Ci/ricr, open, one on each side, into the auricle of the heart. Each is formed by the union of a superior and an inferior vein, named the itrimitive jugular and the cardinal.

The primitive jugular vein receives the blood from the cranial cavity by channels in front of the ear, which are subsequently obliterated : in the greater part of its extent it becomes the external jugiilar vein : and near its lower end it receives small brandies, which, grow to be the external jugular and subclavian veins. The cardinal veins are the primitive vessels which return the blood from the Wolffian bodies, the vertebral column, and the parietes of the trunk. The inferior vena cava is a vessel of later development, whichopens into the trunk of the umbilical and omphalo-mesenteric veins, above the vense heijaticas revehentes. The iliac veins, which unite to form the inferior vena cava, communicate with the cardinal veins. The inferior extremities of the cardinal veins are persistent as the internal iliac veins. Above the iliac veins the cardinal veins are obliterated in a considerable part of their course ; their upper portions then become continuous with two new vessels, the j;osfe?-ipr vertchral veins of Ratlike, which receive the lumbar and intercostal twigi.



Fig. 594. — Diagrams illustrating HE DEVELOPMENT OF THE GrEAT Veins (after KiJlliker).

A, plan of the principal veins of the fretus of about four weeks, or soon after the first formation of the vessels of the hver and the vena cava inferior.

B, veins of the liver at a somewhat earlier period.

C, principal veins of the foetus at the time of the first estabhshment of the placental circulation.

D, veins of the liver at the same period.

dc, the right and left ducts of Cuvier ; ca, the right and left cardinal veins ; j. j,ihe jugular veins ; s, the subclavian veins ; az, the azygos vein ; u, the umbilical or left umbilical vein ; «', in B, the temporary right umbilical vein ; o, the omphalo-meseuteric vein ; o', the right omphalo-mesenteric vein ; m, the mesenteric veins ; p, the jjortal vein ; p', p', the vente advehentes ; I, the ductus venosus ; V, I', the hepatic veins ; c'l, vena cava inferior ; il, the division of the vena cava inferior into common iliac veins ; cr, the external iliac or crural veins ; h, the hypogastric or internal iliac veins, in the line of continuation of the jirimitive cardinal veins.

In C, li, in dotted lines, the transverse branch of communication between the jugular veins which forms the left innominate vein ; ri, the right innominate vein ; ca, the remains of the left cardinal vein by whish the superior intercostal veins fall into the left innominate vein ; above lo, the obliquely crossing vein by which the hemiazygos joins the azygos vein.


As development proceeds, the direction of the ducts of Cuvier is altered by the descent of the heart from the cervical into the thoracic region, and becomes continuous with that of the primitive jugular veins. A communicating branch makes its appearance, directed transversely from the junction of the Jeft subclavian and jugular veins, downwards, and across the middle line to the rig-ht jugular ; and further down in the dorsal region between the posterior verteljral veras a communicating branch passes obliquely across the middle line from right to left. The communicating branch between the primitive jugular veins is converted into the left innominate vein. The portion of vessel between the right subclavian vein and the termination of the communicating branch becomes the right innominate vein. The portion of the primitive jugular vein below the communicating vein, together with the right duct of Cuvier. forms the vena cava superior, while the cardinal vein opening into it is the extremity of the great vena azygos. On the left side, the portion of the primitive jugular vein placed below the communicating branch, and the cardinal and i^osterior vertebral veins, together wdth the cross branch between the two posterior vertebral veins, are converted into the left superior intercostal and left superior and inferior azygos veins. The variability in the adult arrangement of these vessels depends on the various extent to which the originally continuous vessels are developed or atrophied at one point or another. The left duct of Cuvier is obliterated, except at its lower end, which always remains pervious as the coronal sinus. Even the adirlt, traces of the existence of this vessel can always be recognised in the form of a fibrous band, or sometimes even a narrow vein, which descends obliquely on the left auricle ; and in front of the root of the left lung there remains a small fold of the serous membrane of the pericardium, the re.sfii/ial fold of the pericardium, so named by Marshall, to whom is due the first full elucidation of the nature and relations of the left primitive vena cava.


Fig. 595. — A and B. — Diagrammatic Outlines op the Vestige of the Left Superigr Cava and of a Case of its Persistence (sketched after Marshall), h,

A, brachio-cephalic veins with the superior intercostal, azygos, and principal cardiac veins.

B, the same in a case of persistence of the left superior cava, showing its communication with the sinus of the coronary vein. The views are supposed to be from before, the parts of the heart being removed or seen through

1, 1', the internal jugular veins ; 2, 2', subclavian veins ; 3, right innominate ; 3', right or reguhir sujjerior cava ; 4, in A, the left innominate ; in B, the transverse or communicating vein between the right and left superior vemg cavte ; 5, in A, the oj)ening of the superior intercostal vein into the innominate ; 5', vestige of the left superior cava or duct of Cuvier ; 5, 5', in B, the left vena cava superior abnormally persistent, along with a contracted condition of 4, the communicating vein : 6, the sinus of the coronaiy vein ; 6', branches of the coronary veins ; 7, the superior intercostal trunk of the left side, or left cardinal vein ; 8, the principal azygos or right cardinal vein ; 7', 8', some of the upper intercostal veins ; 9, the opening of the inferior vena cava, with the Eustachian valve.



The left duct of Cuvier has been observed persistent as a small vessel in the adult. Less frequently a right and left innominate vein open separately into the right am'icle. an arrangement which is also met witli in birds and in certain mammals, and which results from the vessels of the left side being developed similarly to those of the right, while the cross branch remains small or absent. (Quain on the Arteries, plate 58, figs. 9 and 10.)


Fig. 596. — View op the Foetal Heart AND Great Vessels, from the left SIDE, TO SHOW THE VeSTIGE OF THE Left Superior Cava VEI^f in situ. (This figure is j)lanned after one of Marshall's, and slightly altered according to an original dissection.)

a, right auricle ; b, left auricle and pulmonary veins ; c, the conns arteriosus of the right ventricle ; d, the left ventricle ; c, descending aorta ; + , vestigial fold of the loericardium ; /, arch of the aorta, with a part of the pericardium remaining superiorly ; r/, main pulmonary artery and ductus arteriosus ; [/', left pulmonary artery ; 1,1', right and left internal jugular veins ; 2, 2', subclavian veins ; 3, 3', right innominate and superior vena cava ; 4, left innominate or communicating vein ; 5, 5', remains of the left superior cava and duct of Cuvier, passing at + in the vestigial fold of the pericardium, joining the coronary sinus, 6, below, and receiving above the superior intercostal vein, 7 ; 7', 7', the upper and lower intercostal vein, joining into one.


A case is recorded by Gruber, in which the left vena azygos opened into the coronary sinus, and was met by a small vein descending from the union of the subclavian and jugular. (Reichert and Dubois. RejTnond's Archiv, 18(54, p. 729.) In this case, the jugular veins had been developed in the usual manner, while the left vena azygos continued to pour its blood into the duct of Cuvier.

(Consult Kolliker, Entwickelungsgeschichte, p. 41-1, et seq. ; J. Marshall on the Development of the great Anterior Veins in Man and Mammalia, in Phil. Trans., part i., 1850 ; and Wenzel Gruber, Uber die Sinus Communis und die Valvulaj der Vense Cardiaca3, &c., in Mem. de I'Acad. imper. des Scien. de St. Petersbourg, 1SG4 ; and in Virchow's Archiv, Jan. 1SG6.)


PECULIARITIES OP THE FOETAL ORGANS OP CIRCULATION

It may be useful here to recapitulate shortly the peculiarities of structure existing in the advanced stage of the formation of the foetal organs of circulation with reference to their influence in determining the course of the blood during intra-uterine life, and the changes which occur in them in consequence of the establishment of pulmonary respiration at birth.

The so-called foramen ovale retains the form of a free oval opening in the septum auricularum up to the fourth month, but in the course o"f that month and the next there takes place the growth from below and on the left side of a flat plate or curtain, which advancing upwards fills up the floor of the fossa ovalis, adheres to its left borders as far as its anterior part, and then becoming free and passing beyond the anterior border of the fossa, converts the aperture into an oblique passage or slit over the valvular margin of the fold, so that in the last three and a half months the arrangement is completed, by which blood may readily pass from the right into the left auricle, but not in a contrary direction.

The Eustachian Valve constitutes a crescentic fold of the lining structure of the heart, which is situated to the right of the opening of the inferior vena cava and fossa ovalis, deepens that fossa, and directs the blood entering it from the inferior cava towards the opening of the foramen ovale ; while it throws the opening of the great coronary vein into connection with the right auricle, into which the superior vena cava also opens.

The formation at an early period of foetal life of the transverse vein of the neck uniting the left with the right brachio-cephalic veins, carries the whole of the blood returning from the head and neck, together with that from the main azygos, into the stream entermg the heart by the superior cava.

The ductus arteriosus passes from the main pulmonary artery into the aorta, at the hollow part of the arch, a short distance beyond the place of origin of the left subclavian artery. It is nearly of the same width with the pulmonary stem, while the right and left pulmonary arteries are of comparatively small size, so long as the lungs have not been expanded by air in rfespiration.


Umbilical Vessels

Besides the usual branches of the descending aorta intended to supply the abdominal viscera and the lower limbs, two large vessels, named hypogastric or iimhilical arteries, are prolonged from the common iliacs, and passing out of the abdomen, proceed along the umbilical cord, coiling round the umbilical vein to reach the placenta. The commencement of each of these vessels afterwards forms the tmnk of the corresponding- internal iliac artery, but, from their size, they might be regarded in the fojtus as the continuations of the common iliac arteries into which the aorta divides. From the placenta the blood is returned by the umbilical vem. which, after entering the abdomen, communicates by one branch with the portal vein of the liver, and is continued by another, named ductus rcnosus, into one of the hepatic veins, through which it joins the main stem of the vena cava inferior.

Fig. 597. — Semi-diageammatic view of the Organs of Circulation in the Fcetus FROM BEFORE (from Luschka, modified, and from Nature). |

a, front of the thyroid cartilage ; 6, right side of the thyroid body ; c, trachea ; d, surface of the right lung turned outwards from the heart ; e, diai^hragm below the apex of the heart ; /, right lobe of the liver, dissected to show ramifications of the portal and hepatic veins ; /', the middle part and left lobe of the liver in the same manner, .showing branches of the umbilical veins and ductus venosus ; g, right, fj', left kidney ; ij" , suin-arenal bodies ; h, right, li, left ureter ; i, portion of the small intestine tunied towards the side, to show the veins from it going to the portal vein ; Ic, urinary bladder ; I, is placed below the umbilicus, which is turned towards the left of the fcetus, and points by a line to the urachus ; m, rectum, divided and tied at its upjier part.

A, A. right auricle of the heart opened to show the foramen ovale : a probe, introduced through the large divided right hepatic vein and vena cava inferior, is seen passing through the fossa ovalis into the left auricle : at the lower part of the fossa ovalis is seen the Eustachian valve, to the right and inferioi'ly the auriculo-ventricular orifice ; B, the left auricular appendix ; C, the surface of the right ventricle ; D, placed on the inner surface of the left lung, i)oints to the left ventricle.

1, ascending part of the arch of the aorta ; 1', back part beyond the ductus arteriosus ; 1", abdominal aorta; 2, stem of the pulmonary artery ; 2', the place of division into right and left pulmonary arteries and root of the ductus arteriosus : the left pueumo-gastric nerve is seen descending over the arch of the aorta ; 3, superior vena cava ; 3', right, 3", left innominate vein ; 4, stem of the inferior vena cava, between the junction of the hepatic vein and the right auricle ; 4', continuation of the vena cava inferior below ; 5, umbilical vein within the body of the fojtus ; 5 x , without the bo'ly, in the umbilical cord ; 5', 5', ductus venosus ; between 5 and 5', the direct branches of the umbilical vein to the liver ; 5", 5", hepatic veins, tlu-ough one of which a probe is passed into the fossa ovalis and through the foramen ovale ; 6, vena portD3 ; 6', its left branch joining the umbilical vein; (i", its right branch; 7, placed on the right iliac vein, points to the right common iliac ai-tery; 7', left common iliac artery; 8, right, 8', left umbilical arteries coming from the internal iliac arteries ; 8 x , umbilical arteries without the body, in the umbilical cord ; 9, 9', external iliac arteries ; 10, placed below the right renal vessels ; 11, inferior mesenteric artery, above the root of which .ore seen the two spermatic arteries.


Fig. 597,


Course of the Blood in the Foetus

The right auricle of the foetal heart receives its blood from the two venre cavfe and the coronary vein. The blood brought by the superior cava is simply the venous blood returned from the head and upper half of the body ; whilst the mferior cava, which is considerably larger than the superior, conveys not only the blood from the lower half of the body, but also that which is returned from the placenta through the umbilical vein. This latter stream of blood reaches the vena cava inferior, partly by a direct passage — the ductus venosus, and partly by the hepatic veins, which bring to the vena cava inferior all the blood circulating through the liver, whether derived from the supply of placental blood entering by the umbilical vein, or proceeding from the vena portfe or hepatic artery.

The blood of the superior vena cava, descending in front and to the right of the Eustachian valve, and mixed with a small portion of that from the inferior cava, passes on into the right ventricle, and is thence propelled into the trunk of the pulmonary artery. A small part of it is then distributed through the branches of that vessel to the lungs, and retuins by the pulmonary veins to the left auricle ; but, as these vessels remain comparatively undilated up to the time of birth, by far the larger part passes through the ductus arteriosus into the dorsal aorta, entering that vessel beyond the place of origin of the arteries of the head and upper limbs, and, mixed perhaps with a small quantity of the blood flowing into the aorta from the left ventricle, is distributed in part to the lower half of the body and the viscera, and in part is conveyed along the umbilical arteries to the placenta. From these several organs it is returned by the vena cava inferior, the venaj portsB, and the umbilical vein : and, as already noticed, reaches the right auricle through the trank of the inferior cava.

Of the blood entering the heart by the inferior vena cava, only a small part is mingled with that of the superior cava, so as to pass into the right ventricle ; by far the larger portion, directed by the Eustachian valve through the foramen ovale, flows from the right into the left auricle, and thence, together with the small quantity of blood returned from the lungs by the pulmonary veins, passes into the left ventricle, from whence it is sent into the arch of the aorta, to be distributed almost entu-ely to the head and upper limbs. A small portion of it, may, however, flow on into the descending aorta, and join the fuller stream of blood from the ductus arteriosus. From the upper half of the body the blood is returned by the branches of the superior cava to the right auricle, from which its course into the right ventricle and pulmonary trunk has been already traced.

There is probably a considerable difference in the early and more advanced stages of foetal life, m the distribution of the stream of blood entering the heart by the vena cava inferior. In the early stages, a lai-ge part of the cuiTcnt being directed into the left, but in the three last months, and as the foetus approaches maturity, more and more of the blood of the inferior cava joins the stream from the superior cava ; and, indeed, the coui-se of the blood, and the relative position of the veins, as well as other original peculiarities of the foetal heart, become gradually altered, in preparation, as it were, for the important changes which take place at birth. It seems also probable that very little of the blood propelled from the left ventricle passes into the descending aoi-ta beyond the ductus arteriosus diu-ing those months of foetal life in which the peculiarities of the circulation are most complete.

From the preceding account of the course of the blood in the foetus, it will be seen that, whilst the modified blood from the placenta is principally conveyed to the upper or cephalic half of the foetus, the lower half of the body is chiefly supplied with the blood which has already circulated through the head and upper limbs. The larger portion of the blood, however, which passes into the descending aorta, is sent out of the body to the placenta. This duty is principally performed by the right ventricle, which after birth is charged with an office somewhat analogous, in having to propel the blood through the lungs. But the passage of the blood through the vessels of the umbilical cord and placenta is longer and subject to greater resistance than that of the pulmonary chculation, and the right ventricle of the foetus, although probably aided by the left in the placental circulation, also takes a large shave in the systemic through the lower half of the body ; and this, ijerhaps, may be the reason wliy the wall of the right equals in thickness that of the left ventricle in the fa^tus.

Sabatier was the first to call attention particularly to the action of the Eustachian valve in separating the currents of blood entering the right auricle by the superior and inferior venaj cavse. (Traite d'Anat., vol. ii., p. 22i.) This separation, as well as that occm-ring between the currents passing through the aortic arch and the ductus arteriosus into the descending aorta, were illustrated experimentally by John Reid. (See art. '• Heart," in Cyclop, of Anat. and Phj'siol., and Edin. Med. and Sui-g. Journal, ISo.j.) A striking confirmation of the extent to which the last mentioned division of the two currents of the foetal blood may take place, without distm'bance of the chculation up to the time of bii-th, is afforded by the examples of malformation in which a complete obliteration has existed in the aortic trunk immediately before the place of the union of the ductus arteriosus with the posterior part of the aortic arch.

CHANGES IN THE CIRCULATION AT BIRTH

The changes which occur in the organs of circulation and respiration at birth, and lead to the establishment of their permanent condition, are more immediately determined by the inflation of the, lungs with air in the first respiration, the consequent rapid dilatation of the pulmonary blood-vessels with a greater quantity of blood, and the interruption to the passage of blood through the placental circulation. These changes are speedily accompanied by shrinking and obliteration of the ductus arteriosus, in the space between the division of the right and left pulmonary arteries and its junction with the aorta, and of the umbilical arteries from the hypogastric trunk to the place of their issue from the body by the umbilical cord ; — by the cessation of the passage of blood through the foramen ovale, and somewhat later by the closure of that foramen, and by the obliteration of the umbilical vein as far as its entrauce into the liver, and of the ductus venosus within that organ.

The process of obliteration of the arteries appears to depend at first mainly on the contraction of the coats, but this is very soon followed by a considerable thickening of their substance, reducing ra^mlly their internal passage to a minute tube, and leading in a short time to final closure, even although the vessel may not present externally any considerable diminution of its diameter. It commences at once, and is perceptible after: a few respirations have occurred. It makes rapid progress upon the first and second days, and by the third or fourth days the passage through the umbilical arteries is usually completely interrupted. The ductus arteriosus is rarely found open after the eighth or tenth day, and by three weeks it has in almost all instances become completely impervious.

The process of closure in the veins is slower, there not being the same thickening or contraction of their coats ; but they remain empty of blood and collapsed, and by the sixth or seventh day, are generally closed.


Although blood ceases at once to pass through the foramen ovale from the moment of birth, or as soon as the left auricle becomes filled with the blood returning from the lungs, and the pressure ^Yithin the two auricles is equalised, yet the actual closure of the foramen is more tardy than any of the other changes now referred to. It is gradually effected by the union of the forepart of the valvular fold forming the floor of the fossa ovalis with the margin of the annulus on the left side ; but the crescentic margin is generally perceptible in the left auricle as a free border beyond the place of union and not unfrequently the union remains incomplete, so that a probe may be passed through the reduced aperture. In many cases a wider aperture remains for more or less of the first year of infancy, and in certain instances there is such a failure of the union of the valve as to allow of the continued passage of venous blood, especially when the circulation is disturbed by over-exertion, from the right to the left auricle, as occurs in the malformation attending the morbus coeruleus.


TYPE OF DEVELOPMENT AND ABNORMAL FORMS OF THE GENITAL ORGANS

The type of development of the genital organs may be stated to differ in the several parts of the system in the two sexes as follows, viz. : —

1st. It is single and homological in the external organs.

2nd. It is double and heterological in the middle organs or passages.

3rd. It is partially double and heterological in the productive organs.

Accordingly the congenital malformations of the reproductive organs admit of being distributed under the following divisions : —

1st. Abnormal forms attributable to deficient, redundant, or abnormal modes of development of one or more of the external organs in either sex, producing an approach to the fonn of the other sex.

2nd. Forms referrible to deficient, redundant, or abnonnal modes of development of one or other of the two sets of sexual passages, viz., of the Wolffian or Miillerian ducts, so as to lead to the greater or less predominance of sexual characters in a part or the whole of these passages inconsistent with tliose prevailing in other parts of the system, or to the coexistence of both sets of passages in whole or in i:)art.

8rd. Extremely rare forms referrible to the possible coexistence of the productive parts of testicles and ovaries in the same individual, usually combined with more or less of the foregomg kinds of malformation.

Upon the subject of these malformations the reader may consult the learned and able article Hermaphroditism by Sir James Y. Simpson in the Cyclop, of An at. and Physiol.

Upon the subject of malformations in general the following works are recommended, viz. : —

Isid. Geoff. St. Hilaire, Hist. Gen. et Partic. des Anomalies de I'Organisation, &c., 3 torn. Paris, 1832 — 6 ; Cruveilhier, Anat. Pathol., &c., Paris, 1S;>() — 42. Otto, Sexcentorum Monstrorum desc Anat. Vratisl., 1841 ; Th. L. W. Bischoff. Uber Missbildungen, &c., in R. Wagner's Handworterbuch der Physiol., 1843 ; Wm. Vrolik, Tab. ad illustr. Embryol. Hom. et Mammal, tam Natiu-. quam Abnormem, Amstel., 1849, and the article " Teratology"' by the same author in Todd's Cyclop, of Anat. and Physiol. ; Aug. Forster, Die Missbildungen des Menschen. &c., Jena, 1861 ; as also the systematic works of Rokitanski and others on Pathological Anatomy.

The following tabular scheme of the Coreesponding Parts of the ffenito-urinary organs in the two sexes, and of their relation to the Formative Rudiments of the common embryonic type, may be useful in fixing attention on the more important points of the foregoing description, and indicating more clearly the homologies of the parts : —

Fejule Perjiaxext. Common Embryonal. Male Permanent.


I. -COMMON BLASTEMA OF REPRODUCTIVE GLANDS.

Ovary. Body of Testicle.

Fnniislies the ovigerms and re- 1. Germ-epithelium covering . . Uisuppear.s, and is replaced by mains on the .surface. serous covering of tunica

vaginalis.

Forms stroma of the ovary and 2. Deeper blastema Forms glandular seminal tubes

the Graalian follicles. of the testis.

II.- WOLFFIAN BODIES.

Transverse tubes of epoophoron 1. Upper tubular non-glonieru- Vasa efferentia and coni vas or organ of Rosennuilkr lar part. culosi of the epididymis. (Parovarium).

Paroophoron (Wald.) 2. Lower glomerular part (pri- Paradidymis (Wald.), organ of

mordial kidneys). Giraldes, and ^'asa aberrantia.

Koimd ligament of the uterus . . 3. Ligament of the "Wolffian Gubemaculum testis.

body.

Ill- WOLFFIAN DUCTS.

Tube of the Epoophoron 1. Upper and middle parts .... Convoluted tube of the epididymis.

Ducts of Gaertner, in cow and pig 2. Lower part Vas deferens and vesiculse

seminales.

IV— MULLERIAN DUCTS.

Pimbriated abdominal opening 1. Upiwr extremity Hydatid of Morgagni.

and terminal and oecasiunal hydatids

Paliopian tubes 2. Middle part Occasional tubular pi'olonga ticns (it uterus masculinus.

Vagina and uterus 3. Lower single or meiiian part Uterus masculinus (vesicuU

prostatica).

v.— GENITAL CORD AND SINUS UROGENITALIS.

Tissue uniting female urethra and 1. Substance surrounding geni- Prostate gland. Muscular and vagina. tal cord. glandular tissue.

Female urethra 2. Upper part of cavity or Upper part of prostatic portion

urinai-j' pedicle. of the urethra.

Ostium vaginae . Hymen 3. Confluence of urinary and Verumontanum.

genital ]iarts. Vestibule 4. Lower part Lower ]iart of prostatic portion and membranous part of urethra. Glands of Bartholin 5. Common blastema Cowper's Glands.

VL— EXTERNAL ORGANS.

1. — Vascular parts.

Crura and corpus clitoridis a. Corpora cavern<jsa Crura and corpus penis.

Glans clitoridis and vascular 0. Corpora spongiosa Glans penis and spongy body

bulbs separate) of urethra (united). 2. Integumental parts.

Preputium clitoridis «. On genital eminence Preputium penis.

Integumental folds of nymphee b. Lijjs of genital furrow Integument and raphe below

(separate). . ]ieiiis.

Labia majora (se]iarate) c. Genital ridges (lateraP Scrotum and raphe (united).

Perineum of female, with raphe . U. Transverse interauogcnital Perineum of male beliind

baud. scrotum, with raphe.

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