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|[[File:Mark_Hill.jpg|50px|left]] This historic 1941 paper by Nobaok and Rehman describes the development of the ductus arteriosus in the human fetus and newborn infant.

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=The Ductus Arteriosus in the Human Fetus and Newborn Infant=

Gustave Joseph Nobaok And Irving Rehman


Departments of Anatomy, College of Dentistry and The Graduate School of Arts and Science, New York University

Three Plates (Twelve Figures)

==Introduction==

Descriptions of the course and topography of the ductus arteriosus in the human fetus and newborn child as recorded in the literature were found to differ markedly from the findings of the senior author as reported in the symposium on Recent Developments in Anatomy at the fifty—third meeting of the American Association of Anatomists held at Toronto, in 1938. The present report comprises a study of 100 fetal and full—term stillborn cadavers made for the purpose of determining the anatomy of the ductus and its relation to its surrounding structures. As a result of the many observations carried out, the gross anatomy of the ductus is herein more accurately recorded.

==Literature==

The first known mention of the term “ductus arteriosus” occurs in the works of Guilio Cesare Aranzi in his “De humano foetu liber” published in 1595, 6 years after his death. However, the ductus was na.med after a contemporary, Leonardus Botallus, (1565), who discussed the fetal circulation. Harvey (1628), also observed the ductus for he described it “as a kind of arterial canal, carried obliquely from the vena arteriosa, or pulmonary, to perforate and terminate in the arteria magna or aorta”.


Very little attention was directed toward the ductus until Kilian (1826) observed that in the 4 to 6 week embryo the aorta and pulmonary artery are of the same construction but separated from each other for a small distance only. The adjacent side walls of both vessels which grow from below upward form a common projecting wall at the union of the ductus and aorta. Strassmann (1894) referred to a valve-like structure at this point and evidently based his observations partly upon those of Kilian.

The ductus was described by Kilian as sloping obliquely upward from right to left and being slightly bent in its course from before backward. The angle formed by the entrance of the ductus into the aorta was Very acute; the ductus lying alongside the aorta for a short distance and united to it by cellular material. The diameter of the lumen of the ductus was found to be that of a “quill” and therefore subject to a great deal of variation. The lumen of the ductus decreased in diameter toward the aorta and its entrance into the aorta occurred where the recurrent laryngeal nerve curved around the aorta. The subclavian artery arose three to four “linien” (line -—= 1/1;» inch) to the right of this. Therefore the aorta, to the left of the origin of the subclavian artery, did not form the aortic arch but actually formed the ductus arteriosus. A narrowing of the lumen of the aorta occurred distal to the origin of the subclavian artery and after receiving the ductus the lumen of the aorta widened again. These observations of Kilian, which are apparently inaccurate, formed the basis of several theories of closure put forth by subsequent workers. Langer (1857) maintained that a great difference in structure existed between the pulmonary artery, aorta and ductus in the 5 and 7 month old fetus. However, no noticeable difference in thickness of different parts of the wall of the ductus existed. In the full-term stillborn the walls of the ductus were stronger than those of the pulmonary artery and aorta and thicker on one side. Since the course of the ductus was oblique, the margins of both conical lumina lie against the aorta anteriorly at the aortic end and against the right pulmonary branch at the pulmonary end.

Walkoff (1868) also described the ductus as the continua— tion of the pulmonary artery coursing obliquely upward, laterally and posteriorly to terminate at an angle in the medial part of the aorta about 3 to 4 mm. from the origin of the left subclavian artery.

The ductus was described by Wrany (1871) as a conical, reduced continuation of the pulmonary artery. His description of its course and entrance into the aorta was similar to that of Kilian. The ductus passed for some millimeters of its course over the surrounding fold of pericardium in the posterior mediastinum and lay imbedded in very loose connective tissue.

Strassmann (1894) reported that the ductus arose from the pulmonary artery and continued superiorly, laterally, and posteriorly to enter the concave underside of the aorta; that the diameter of the ductus was almost equal to that of the aorta and in their course the two vessels almost paralleled each other; and the entrance occurred a little below the origin of the left subclavian artery where the arch of the aorta continued as the descending aorta therefore forming a very acute angle. The ductus arteriosus, a continuation of the pulmonary artery, was not demarcated from the pulmonary artery by any folds; the two pulmonary arteries therefore appeared to be side branches of the main pulmonary trunk and its continuation, the ductus arteriosus.

Strassmann described the changes occurring in man toward the end of the eighth month as preparations for the mechanical closure of the ductus. The ductus courses in an “unopened arch-shaped curvature to its oblique entrance into the aorta whose wall covers over the elliptical slit-like opening in a valve-like fold very little developed” (fig. 1). The change in position of the ductus and the aorta was found to be only relative in the ninth and tenth fetal months until birth. An increase in caliber did occur; the growth of the ductus being as rapid as the pulmonary arteries. The ductus reached its maximum size at birth; but the projection of the ductus into the aortic wall could only be noticed in the empty condition. The ductus now opened into the inferior and lateral wall of the aorta where it becomes the descending portion. The covering of the aortic entrance of the ductus by the projection of the anterior wall of the aorta was easily seen by Strassmann. The opening of the ductus into the aorta progressively changed from the fifth month to birth, becoming more slit-like, over which opening there developed a ridgelike or “valve-like” projection of the proximal half of the arch in the newborn. This was formed by means of a duplicature of the anterior wall of the ductus with the aortic wal.l.

According to Chievitz (1899) the pulmonary artery, after giving off the right and left pulmonary branches from its posterior aspect, passes posteriorly in a. horizontal and nearly sagittal plane as the ductus arteriosus. After a short course the ductus joins the aorta, being crossed at the point of junction by the vagus nerve.

Kuschew (’01) found that the ductus arose from the bifurcation of the pulmonary artery in 92.6% of the cases and terminated in the inferior wall of the aortic arch where it becomes the descending aorta. The aortic entrance of the ductus was located about 2 to 3 mm. below the origin of the left subclavian artery.

Roeder (’O2) was the first investigator to measure the angle formed by the entrance of the-ductus into the aorta. This angle which he found to be 30 degrees formed the basis of his explanation of the fetal type of circulation.

Stienon (’12) described the ductus in the newborn as the direct continuation of the pulmonary artery ascending to the left, crossing the left pulmonary artery to terminate in the antero-internal part of the descending aorta beneath its point of union with the isthmus. This relationship has not once been observed in the present study.

According to Faber (’12) the ductus before birth is a thick tube that is straight and continuous with the pulmonary artery running obliquely from above to its opening into the aorta.

Grundobin (’12) also reported that the ductus arises from the point of bifurcation of the pulmonary artery and in some cases from the left pulmonary. However, he was unable to find any case in which the ductus arose from the left pulmonary artery and therefore one is led to infer from this statement that he is quoting the work of some other investigator, probably Kuschew. The entrance of the ductus into the aorta was found to lie in the lower wall (“untere Wand”) of the descending part of the aorta. The length and thickness of the ductus decrease some days after birth.

Linzenmeier (’14) studied a series of stillborns, and 4- and 5-day old newborns. The ductus in the newborn that had not breathed was almost a direct continuation of the pulmonary artery, conically tapering in its course posteriorly to the left, and arching slightly lateral and anteriorly to enter somewhat medially into the anterior wall of the descending aorta at an angle of about 30 to 40 degrees. The place of entrance into the aorta is about 0.5 cm., below the entrance of the left subclavian artery.

Dwight (1881), Symington (1887), Fetterolf and Gittings (’11) and Grittings, Fetterolf and Mitchell (’16) described the topography of the thoracic viscera in infants but made no mention of the ductus. The latter described the thymus as relatively large and extending beyond the borders of the sternum, widely separating the upper lobes of the two lungs and also make mention of a solid mass of tissue between the thymus and the trachea. The posterior and lateral extent of the thymus is not described in any greater detail.

A more detailed study of the thymus and its topographic relations was carried out by N oback (’21). Upon examining sixty-five fetuses and full-term infants ranging from 10 to 55 cm. in crown heel length, he found that the lobation of the thymus was determined in early fetal life. The thymus in the late fetus was found to be predominantly cervico-thoracic in location; the position being intermediate between that of 510 GUSTAVE JOSEPH NOBACK AND IRVING REHMAN

the cervical location in the embryo and thoracic position in later life. The lateral surfaces of the thymus in the stillborn are convex and in contact with the medial surfaces of the lungs, but the lungs rarely extend on to the anterior surface.

In the newborn that has breathed the thymus becomes elongated and moulded as a “result of compression” by the neighboring structures, “Competition for Space”, Noback (’37), the lungs now extend over the lateral part of its anterior surface. This change in form from the broad or fetal type to the elongated, moulded type of the liveborn infant is directly dependent upon the establishment of respiration and the degree of expansion of the lungs. As a result of this expansion of the lungs “the thymus is compressed on both sides by the medial surfaces of the expanding lungs and also antero— posteriorly by the anterior borders of the lungs which early become much thickened in the establishment of respiration and gradually overlap the thymus” (Noback, ’21).

Noback also found that in “some cases the thymus may extend posteriorly to such an extent that structures there are compressed by it. This may be due either to an unusually large thymus or to a very narrow, superior thoracic aperture which will not allow the thymus to protrude into the cervical region as it is compressed by the expanding lungs”. The changes in form and topography of the structures in the thorax as a result of the expansion of the lungs must be considered in any explanation of the factors involved in the closure of the ductus.

Griiper (’21) observed that the pulmonary trunk continued as the ductus; bending gradually in its course so that no acute bending (“knickung”) resulted. The course of the ductus was concave below and underwent the greatest bending in the middle, being bent toward the left and lying close to the aortic arch. The opening into the descending aorta at an angle of 30-33 degrees according to Roeder (’02), was such that the ductus and aorta were fused at the entrance of the ductus and therefore resembled a valve (Strassmann) when cut in longi tudinal section. 

Dragendorf (’29) found that the aortic arch in the newborn is ﬂatter than in later life and the ductus is placed directly against the aortic arch in the newborn. At its beginning the ductus forms a continuation of the pulmonary trunk and then continues in a ﬂat, upward bending arch and enters the descending aorta below the isthmus at an angle of 33 degrees (Roeder). The aortic entrance is oblique and therefore oval.

MATERIALS AND METHODS

The series of 100 fetal, newborn and infant cadavers used in the study ranged in age from 5 fetal months through the period of the newborn. Anthropometric observations were made prior to embalming by injection into the umbilical vein of a 10% solution of formalin. Infants weighing between 2500 to 3500 gm., ranging between 45 to 50 cm. in crown-heel length and having a thoracic index between 86 and 100 were considered newborns according to the standard formulated by Scammon and Rucker (’21).

The material was prepared for dissection by imbedding each cadaver on its back in wax to the level of the mid-axillary line. The exposed parts of the body were also covered with wax and the wax removed as the dissection progressed. The purpose of imbedding in wax was twofold: (1) to prevent any movement and distortions due to handling and, (2) to minimize changes due to drying. Needles were imbedded in the forehead, shoulder and symphysis pubis, about 2 mm. of the needle remaining exposed above the surface to serve as orientation points in lining up the orthoscopic drawing with the specimen or to superimpose the successive drawings. An orthoscopic drawing (by means of the apparatus designed by Herbelsheimer and modified and improved by Noback, ’28) was made, photographs were taken and casts were made of each stage of the dissection. The materials used and the technique employed in casting were described in detail by Rehman and Noback (’37). Casts of some of the serial dissections were demonstrated at the fifty-first and fifty-third annual sessions of the American Association of Anatomists (Noback and Rehman, ’35, ’37).

Anterior approach. Photographs and orthoscopic drawings to serve as a record of the condition of the specimen were made. The skin, pectoral and intercostal muscles were removed and the sternum, costal cartilages and ribs cleaned as far posteriorly as possible. This stage of dissection was recorded by means of photographs, drawings and casts. The muscles of the neck attaching to the manubrium sterni and clavicle were detached next and reﬂected upward to expose the cervical portion of the thymus, the thyroid, trachea, carotid vessels, vagi and recurrent laryngeal nerves. The superior extent of the thymus and its relation to the thyroid gland was thus clearly shown. The anterior and lateral portions of the thoracic cage were next removed and the reﬂections of the pleura were recorded. Then the pleura and areolar tissue were removed, the thymus cleaned and drawings, photographs and casts made. The lungs were removed by cutting through their roots; the thymus and pericardium allowed to remain in situ in order that the relations of the thymus to the pulmonary artery and ductus arteriosus might be determined. The thymus and the pericardium were then removed and the heart, great vessels and ductus cleaned, drawn, photographed and cast.

Lateral approach. A lateral exposure of the ductus arteriosus was made by the removal of the left upper extremity, the thoracic wall in this region and the upper lobe of the left lung. Cleaning, measuring and the determination of the topographic relationships of the ductus arteriosus were thus greatly facilitated.

Posterior approach. Removal of the posterior thoracic wall clearly exposed the relationships of the ductus arteriosus to the thymus, heart, upper lobe of the left lung, trachea, descending aorta, etc., from the posterior aspect. 

==Discussion of the Morphology and Topographic Relations of the Ductus Arteriosus==

In the examination of our material with reference to the topography of the ductus arteriosus the present study of a greater number of specimens of the fetus, stillborn and newborn in regard to the form and relations of the thymus, extent of the pleural reﬂections and degree of expansion of the lungs during the period of the newborn is in agreement with the findings of Noback (’21, ’23, ’26). The present study also substantiates his previous observations that the thymus is broad in the fetus and newborn and becomes narrower with increase in age, extending laterally and posteriorly in the newborn in which the lungs have not yet fully expanded. The thymus fills the available space and is molded by the surrounding structures even though the space in the thorax increases as a result of .the elevation of the sternum and ribs with the establishment of respiration. This added space is apparently insufficient and as a result of the expanding lungs, the thymus is molded even further. With the onset of respiration the lungs (Which previously were located in the posterior portions of the pleural cavities) expand and extend medially and anteriorly over the thymus and occupy more of the pleural cavities. This need for more space by the expanding lungs is supplied by changes in form of the thoracic organs. The heart which is relatively solid and fixed in position.by the pericardium and roots of the great vessels, is rotated slightly anteriorly, inferiorly and medially. The thymus, aortic arch, innominate artery, trachea and esophagus show evidence of the pressure of the lungs as evidenced by the change in form of these organs upon post-mortem examination. As a result of this “competition for space” (Noback, ’37), the thymus becomes elongated and forced superiorly through the superior thoracic aperture, and posteriorly and medially against, and in some cases between, the great vessels. However, he failed to note, at that time, that pressure is also brought to bear upon the ductus arteriosus by the thymus and expanding lungs (fig. 2). 


The morphology and topography of the ductus arteriosus as recorded in the literature is not in accordance with our findings. Its size is much larger than is generally assumed, being equal to or greater in caliber than the aortic arch or the descending aorta. It does not course superiorly and laterally to the distal end of the arch of the aorta, but instead tends to parallel the aortic arch and upper part of the descending aorta running more directly antero-posterior as it bulges markedly to the left to terminate in the descending aorta about 1 cm. distal to the origin of the left subclavian artery. The ductus enters the descending aorta on its antero-lateral aspect and therefore overlaps its aortic entrance and it is longer than is usually stated. The relations of the ductus to its adjacent structures have been incorrectly described by previous investigators because of inaccurate or insufficient observations. The intimate relations of the ductus with the bronchus medially, with the left lung laterally and especially with the thymus anteriorly, superiorly and laterally are of paramount importance in any study of the morphology or physiology of this part of the circulatory system.

The thoracic portion of the thymus is covered laterally by pleura, a median area varying in width between 12 mm. superiorly at the jugular notch of the sternum to 4 mm. at the inferior border of the thymus remains uncovered. This uncovered area is due to the failure, as yet, of the pleural reﬂection to meet medially as in the adult (Noback, ’21, ’23) (fig. 3). When traced inferiorly, the pleural margins are separated by a distance of 8 to 20 mm. This is at variance with the statement of Tanja (1891) and others who record that the medial margins of the pleural sacs usually meet behind and toward the left of the midline of the body of the sternum and that this approximation extends behind the entire length of the sternum.

The anterior border of the left lung is situated at a greater distance from the midline than is the right lung and is very deeply notched in its middle half so that a large area consisting of the left surface, apex and left ventricle of the heart remains uncovered by this lung. It is smaller and extends further posteriorly behind the heart than does the right lung. The vertebral portion of the left lung extends posteriorly and medial to the thoracic aorta and bears on its mediastinal sur— face a groove made by this vessel. Anterior to this aortic groove there extends medially a longitudinal ridge of lung tissue which fits into a sulcus between the aorta and the distal part of the ductus arteriosus Where the latter enters the aorta. With the onset of respiration the expansion of the upper lobe of the left lung causes this ridge of lung tissue to extend further medially, probably bringing about a shifting medially of the distal part of the ductus which thus further overlaps its entrance into the aorta. With continued expansion of the lung this groove is deepened causing further narrowing of the elliptical aortic entrance of the ductus into the descending aorta. This sulcus is present in all the specimens studied and appears to be more pronounced in the infants which have breathed (fig. 4).

The thymus presses anteriorly against the manubrium sterni and posteriorly against the superior vena cava, left innominate vein, innominate artery, trachea and esophagus; all these structures show definite post—mortem evidence of this compression (fig. 5). The thymus also rests on the roots of the great vessels, the arch of the aorta, and the portion of the ductus arteriosus immediately distal to the bifurcation of the pulmonary artery (fig. 6). The resistance of the thymus forms a deep impression on the mediastinal surface of the left lung.

In many specimens, the thymus sends a process posteriorly between the superior vena cava and ascending aorta (fig. 7). The anterior part of the ascending aorta is partially covered by the thymus on the left, and anteriorly by the main trunk of the pulmonary artery, the thymus bearing corresponding impressions. The entire left aspect of the ascending aorta is therefore in contact with the root of the pulmonary artery. The pericardium covering the roots of the great vessels is reﬂected from the ascending aorta immediately proximal to the origin of the innominate artery.

The arch of the aorta, situated anterior to the trachea, esophagus and recurrent laryngeal nerve, is separated anteriorly by pericardium from the thymus; the thymus extending posteriorly and laterally to the left‘ of the arch as far as the origin of the subclavian artery. The medial surface of the left lobe of the thymus therefore presses against the aortic arch on the left, causingla ﬂattening of the arch (fig. 8). The left lung lies in contact with the remainder of the aortic arch and with the descending aorta.

The innominate artery which arises from the arch of the aorta to the left of its junction with the ascending aorta is to the left of the trachea in the infant and not anterior to it as in the adult (N oback, ’21) (fig. 9). It is covered at its origin by the left innominate vein and it passes superiorly and laterally to the right over the anterior surface of the trachea. Its course is indicated by an oblique groove it makes on the trachea as seen in every specimen examined. The cervical portion of the thymus presses posteriorly upon the left innominate vein and artery causing the latter to become ﬂattened antero-posteriorly Where it crosses the trachea. N oback noted that the pressure of the thymus was great enough in some infants to cause a marked ﬂattening and shifting on the innominate artery and esophagus to the left, the trachea always being grooved by the innominate artery and often being displaced to the right. This is illustrated here in figure 9.

The direction and course of the arch of the aorta is almost directly antero-posterior and only slightly to the left. Its direction changes only with increase in age, becoming more oblique laterally. The angle made by the arch of the aorta with the frontal plane in its course laterally and posteriorly is about 80 degrees in the newborn and changes to 50 degrees in the 1 year old child (fig. 10). The arch of the aorta is crossed by the left vagus and recurrent laryngeal nerve where it becomes continuous with the descending aorta. The left vagus nerve crosses the ductus arteriosus near its entrance into the descending aorta. The recurrent laryngeal nerve crossed the arch of the aorta proximal to the vagus and the ductus almost midway between its pulmonary and aortic ends. The first part of the left- recurrent laryngeal nerve is therefore in relation to the aorta and ductus medially and the left bronchus and left pulmonary artery inferiorly. After passing medially around the ductus arteriosus the left recurrent laryngeal nerve courses superiorly, the left bronchus being medial, and the ductus arteriosus and arch of the aorta lying lateral to it. The bifurcation of the trachea is directly behind the arch and the left bronchus proceeds inferiorly and laterally inferior to the ductus. The arch continues to the left as the descending aorta and lies to the left of the Vertebral column and the esophagus.

The pulmonary trunk proceeds upward, slightly to the left, almost paralleling the beginning of the arch of the aorta (fig. 11). It ascends toward the left and crosses anterior and superior to the left auricle upon which it rests. The right and left pulmonary arteries leave the pulmonary trunk opposite the origin of the innominate artery. Since its branches leave the pulmonary trunk close to the mid-line the pulmonary trunk is shorter and the ductus arteriosus is longer than usually described. The aorta becomes separated from the pulmonary artery immediately proximal to the bifurcation of the pulmonary artery by loose connective tissue and remains separated from its continuation, the ductus, until the latter enters the descending aorta 1 cm. or more distal to the origin of the left subclavian artery and not opposite the subclavian artery as usually stated.

The branches of the pulmonary artery arise from the lateral and posterior surface of the main pulmonary trunk and continue laterally and -inferiorly to the right and left lungs. The ductus arteriosus is directly superior to the left pulmonary artery. The left pulmonary arteryat its origin lies antero-lateral to the left bronchus upon which it rests as it crosses to the root of the lung and left auricle is posterior to it. The superior or upper left branch of the left pulmonary artery, and the bronchus, are not in direct contact with, but are inferior to the ductus arteriosus.

The left bronchus is directly inferior. to the ductus and passes inferiorly and laterally to the left under the arch formed by the ductus as it passes over it. The recurrent laryngeal branch of the vagus nerve turns medially around the ductus and lies between it and the bronchus. The left bronchus in its course to the root of the lung crosses over the vagus which lies posterior to it.

The course of the ductus arteriosus from the pulmonary artery to the aorta is not upward and to the left. It does not terminate in the distal part of the aortic arch as maintained by Strassmann and others. The ductus arteriosus courses postero—laterally to the left to its entrance into the antero— lateral aspect of the descending aorta about 1 cm. distal to the origin of the subclavian artery and at an angle less than 30 to 35 degrees (fig. 12). Not only is the ductus longer than usually described, but the marked lateral bulge it makes in its arched course to the descending aorta has also been overlooked. figure 10 illustrates this marked lateral bulging of the ductus to the left. The entrance into the aorta therefore is not “at the medial border just below the origin of the left subclavian artery” (Scammon, ’23). The ductus is the direct continuation of the pulmonary artery; in no specimen was a definite “delimiting point between the ductus arteriosus and pulmonary artery” observed as stated by Faber (’12). Superior to the ductus and usually separated from it by a small crescent-shaped, connective tissue filled space lies the arch of the aorta. The proximal part of the descending aorta lies posterior to the distal portion of the ductus. The ductus is in relation inferiorly to the left pulmonary artery, recurrent laryngeal nerve, left bronchus and vagus nerve proceeding antero-posterior. To the left, the ductus is in relation to the thymus anteriorly and superiorly, the recurrent and vagus nerves and left lung laterally and posteriorly. The ductus rests upon the left bronchus medially and inferiorly; and the medial surface of the upper lobe of the left lung presses laterally against and contains an impression formed by the lateral bulge of the ductus. It is interesting to note that Noback (’25) reported that the greatest increase in growth of the lung is transversely (width), and antero-posteriorly even before respiration sets in. Thus the ductus obtains the space it “needs” at the expense of the lungs. From this it may be deduced that when the left lung expands it will exert sufficient pressure against the lateral wall of the ductus and thus reduce the caliber of its lumen.

Upon cutting a window in the lateral wall of the ‘ductus a transverse ridge was noticed projecting into its lumen. This ridge which may be designated a valve, usually found midway between the pulmonary and aortic" ends of the ductus (occluding as much as one-half of the lumen) was found to be present in 25% of the specimens examined macroscopically as reported by N oback (’37 ).

Any attempt at an understanding of the morphology or physiology of the circulatory system and its changes incident to transition from intra-uterine to extra-uterine life necessitates a consideration of these newer anatomical findings herein first presented.

==Summary and Conclusions==

# The description here presented of the topographic relationships, size, shape and course of the ductus arteriosus in the human fetus and newborn is at variance with the literature.
# The size of the ductus is much larger than is generally assumed, being equal to or greater in caliber than the aortic arch, the pulmonary artery, or the descending aorta.
# The course of the ductus is more directly antero-posterior, highly arched, and parallels that of the aorta. It bulges markedly to the left and extends further inferiorly than is usually stated.
# The ductus arteriosus enters the descending aorta on its antero-lateral aspect and not into the medial surface of the arch of the aorta as recorded in the literature. 
# The ductus enters the descending aorta 1 cm. distal to the origin of the subclavian artery instead of just opposite to its origin as usually described in the literature.
# Macroscopic examination of the interior of the ductus revealed a transverse ridge or valve projecting into its lumen and situated about midway between the pulmonary and aortic ends in about 25% of the material. It is not located at the aortic entrance of the ductus where Strassmann (1894) maintained there existed a valve-like ﬂap.
# The ductus arteriosus is covered superiorly, and frequently laterally by the thymus, which organ in turn is covered laterally and anteriorly by the medial surface of the left lung.
# The left lung and thymus press the ductus against the left bronchus. The lung also compresses the oblique anterolateral entrance of the ductus into the aorta so that a deep groove is formed at this junction. The upper lobe of the left lung contains a ridge of lung tissue that fits into this groove.
# A competition for space a.mong the thoracic viscera exists during fetal life which is intensified during the establishment of respiration. The thymus is compressed by the lung and is forced against the ductus and the mediastinal surface of the upper lobe of the left lung presses directly against the ductus as is always indicated by the groove made by the ductus in the lung.

==Literature Cited==

ARANTIUS, GIUL10 CESARSE (1530-1589) De humano foetu liber.

BOTALLUS, LEONARDUS 1660 Opera omnis medica et chirurgica, Lugdun. Batav. Postrema. editione, from Joannis von Horne.

CHIEVITZ, J. H. 1899 A research on the topographic anatomy of the full-term fetus in-situ. Copenhagen.

DRAGENDORFF, O. 1929 Gefasssystem, Apparatus vasorum. In Peter’s Handb. d. Anat. d. Kindes. Bd. II, 2nd Lief., S. 259.

DWIGHT, T. F. 1881 Frozen sections of a. child. New York.

FABER, A. 1912 Die anatomischen und physikalischen Vsrhéiltnisse des Ductus Botalli. Arch. f. Anat. u. Entwicklungsgeschichte.

Fmrrnxow, G., AND J. GITTEKNGS 1911 some anatomical features of the child ’s thorax. Amer. J. Dis. Child., vol. 1, pp. 6-25.

GITTINGS, J ., G. Fmvrmonr AND MITCHELL 1916 A study of the topography

of the pulmonary fissures and lobes in infants. Amer. J . Dis. Child., vol. 12, pp. 6-25. DUCTUS AHTERIOSUS OF FETUS AND NEVVB()RI\'

GRKPER, L. 1921 Die anatomischcn Ve.riindci'ungeii kurz nach dcr (loburt, III Ductus Botulli. Zcitschrift f. Aunt. u. Entwicklungsgeschichte, Bd. 61, S. 312-330. GrUNDOBIN, N. P. 1912 l)ie Bcsondcrheiten (los Kinclesalters, scitc 80, Berlin. HARVEY, VVM. 1628 The works of William Harvey‘, Sydenhnm Socioty, 'l‘r:1ns]:1— tion, London, pp. 38 and 570, 6th chap. KJIJAN, H. F.‘ 1826 Ueber den Krcislauf dos Blutes im Kinde wclche nicht geathmet hat. l\'US('H1<:.\\', N. E. 1.90]. llbcr den Duetus Botnlli bci Kindcrn, Diss. St. Petersburg. (Quoted from J ahresber. fiber die Fortschr, der Anat. 11. Ent.wg., vol. III, S. ‘lF6—163), and from Gundobin “Die Besondcrheitin dos Kindesalters” (1912). LANGER. C. 1857 Zur Anatomic (lcr fetalen Kreislauforgane, Wochenb]. d. zeitschr. der K. K. Gesellseh. der Krztc zu Wein, J. 13, S. 328—339. LINZENMEIER, G. 1914. Der Vcrscliluss dos Ductus arteriosns Botalli much der Gcburt des Kindes. NORACK, G. J. 1921 A contribution to the topographic anatomy of the thymus gland, with particular reference to its changes at birth and in the period of the newborn. Amer. J. Dis. ('Jhild., vol. 22-, pp. 120-144. NOB.-xcrx’, G. J. 1923 The developmental topography of thc larynx, traclioa and lungs in the fetus, newborn, infant. and child. Amer. J. Dis. Child., vol. 26, pp. 515-1533. 1925 The lineal growth of the rcspiraitory system during fetal and neonatal life as expressed by graphic :inul)'sis and empirical formulae. Amer. J. Anat., vol. 36, pp. 235—273. 1926 The thymus in the newborn and early infancy. Radiology, Nov. 1926, pp. 2-4. 1928 A spring pencil addition to Sca1nmon’s orthoseopic apparatus for graphic reconstruction. Anat. Rec., vol. 38,.p. 70. 1935 Changes in relations and form of the ductus artcriosus during early infancy. Anat. l{ce., vol. 6] (Suppl. no. 2), p. 60. 1937 Report at 53rd l\loeting of the American Associntioli of Anatomits. Anat. Rec., vol. 67, no. 4. N01!/\(“K, G. J., AND I. REI-IMAN 1935 Growth and topograpliic eliangos of the thorax, abdomen and pelvis (luring infancy and childhood. An:-it. Roc., vol. 61 (Suppl. no. 2), p. 60. Rm-IMAN, I. 1937 Topogrzlpliy of the (luctns urtcriosus in the fetus, newborn and young infant. Annt. Roc., vol. 67 (Suppl. no. 3), p. 40. REHMJAN, I., AND G. J. NOBACK 1937 An inexpensive casting material for making anatomical reproductions. Aunt. Rec.., vol. 67 (Suppl. no. 3), pp. 493-497. ROEDER, H. 1902 Die Histogeneso (les nrteriellcin (iiingc. Arch. f. Kinderhcilkd., Bd. 33, S. 147-161. Sc/\1u1\IoN, R. E. 1923 A summary of the anatomy of the infant and child. Abt ’s Pediatrics, vol. 1, pp. 257-444. $r*AMMON, R. E., AND W. II. RUC‘l\'ER 1921 Changes in form and dimensions 01‘ the chest at birth and in the noonntnl period. Amer. J". ‘Dis. Chihl., vol. 21, pp. 552-564. 

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WRANY, A. 1871 Der duetus arteriosus Botalli in semen plxysiologist-.l'mn mnl putlmlogisclxelr Verhiiltnissen, Osterr. Jahrb. f. Piidiut., Bd. 1, 821-24.

==Plates==

===Plate 1===

1 Copy of Strass1n:um’s figme 2 showing the co1u's<'- of the (luetus n1'te1'iosus in the newborn human. The valve of the duetus urtoriosus (V.l.).A.) is plzu-,e(l at the aortic entrance of the ductus.

2 The medial surface of the left lung showing the areas in contact with neighbori11g str11ct11res. Note impressions caused by the thymus and duetns arteriosus (D.A.) in the newborn l1un1:1n.

3 Tlroracic cage removed, showing pleural reflections (P1). The extent of thethymus cor-vically onto the trachea ('l‘r.) c-m1 be seen. 1*‘ull-term newborn, human.

4 Left lateral view showing the ductus overlapping its aortic entrance and forming a deep lateral groove. The vagus nerve (V.N.) and its recurrent laryngeal branch (R.L.N.) pass over the pullnonary trunk (P.’l‘r.) and ductus. The d1lctu.~z lies above the loft pulmonary artery (L.P.A.) and left bronchus (L.Br.). "Fullterm newborn, human. “X” indicates the sulcus between the ductus nrterlosus and the descending aorta. 

===Plate 2===

2) The thymus has been lifted to show the structures lying within or behind it. The innominate vein (In.V.) is inelosed in thymus. Newborn.

6 The upper lobe of the left 1u11g has been pulled down to expose the thymus (Tl1y.), phrenic nerve (Pl1.N.) and ductus arteriosus (I).A.). The thymus presses against the sternum (St..) anteriorly and the ductus posteriorly. I-‘ull-term newborn.

7 Left. lung removed showing posterior extent of the thymus behind the innominatc vein (1n.V.) to the left common carotid a1't.ery (L.C.C.).

8 Left lateral view showing ﬂuftellillg of arch of aorta (Ao. Arch). Note

the arcli formed by the ductus over the left bronchus (l..B1'.).

===Plate 3===

9 The origin of the innominate artery (ln.A.) is further to the left of the tracliea (T12) and eourses obliquely to the right. over t.he trachea. in the newborn. l0 Posterior View of t11e t,ho1'-.1ei(-. structu1'es. ’I‘he esophagus has been cut to expose the t1-aellea. to the right. Note the oblique, left lateral entrance of the (lnctns into the descending iiorta. The (lnetus arches over the left bronchus (L.Br.).

11 Aiiterolnteral view; the thymus has been lifted and left lung rernoverl. The ductns proceeds obliquely z111tero—posteriorly and is separated from the aortic arcli so that :1; small space exists between the two.

12 Drawing of the ductus nrteriosus pl:1ced in the same plane as that of Strassmann (see fig. 1). The duetus tends to parallel the aortic arch and contains a. trzulsverse ridge or valve (V.I).A.) projecting into the lnmen of the (luctns almost, midway between the puhnonziry artery (P.A.) and aorta (Ao.). 

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