Paper - The development of the pulmonary vein in the domestic cat (1913)
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Brown AJ. The development of the pulmonary vein in the domestic cat. (1913) Anat. Rec. 7(9): 299-330.
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The Development of the Pulmonary Vein in the Domestic Cat
Alfred J. Brown
Anatomical Laboratory, Columbia University
- Expense of illustrations borne by author.
A review of the literature concerning the pulmonary vein reveals the fact that the various investigators have been divided into two groups according to their method of dealing with the subject. On the one hand the older writers, such as Reisseisen (1), Sommering (2), Zuckerkandl (3) and J. F. Meckel (4) regarded the vein simply as part of the general vascular complex and consequently described its morphology with relation both to other portions of the pulmonary system and to the systemic circulation. The later investigators, as Schmidt (16), His (17), Born (18), Rose (19) and Fedorow (22) have studied the morphology of the vein as such, without reference to its relation to or possible connection with, the extrapulmonary vascular system. They have thus not defined the proper position of the vein in the vascular complex. The first important contributions were those of Reisseisen (1) and Sommering (2). They established the fact that the bronchial and pulmonary veins communicate freely within the lung and that the bronchial veins empty, either directly or through subordinate branches, into the azygos and hemiazygos veins and thus into the systemic circulation. J. F. Meckel (4) accepted the results of Reisseisen and Sommering, and further noted instances in which the pulmonary veins communicate through large or small radicles with the systemic circulation. He states: Hochst merkwiirdig ist es, class nicht bloss in diesem feinen Gefassnetze (i.e. on the surface of the lung), sondern auch zwischen den grosseren Zweigen und Asten der Lungen- unci Luftrohrengef asse bedeutende Anastomosen Statt finden. Die Bronchialvenen senken sich sogar grosstentheils in die Lungen blutadern, nur die an der Wurzel der Lungen befindlichen treten zu kleinen Stammen zusammen, welche sich in die unpaarige Vene oder die obere Hohlader, oder untergeordnete A\ste des Korpervenensystems einsenken. Aus dieser Anordnung ergibt sich daher: 1. dass auch im normalen Zustande in den Lungen sehr bedeutende Communicationen zwischen dem Systeme des rothen und clem des schwarzen Blutes Statt finden; 2. dass die als Abweichungen bisweilen erscheinenden, wo grossere Gefasse der entgegensetzten Systeme sich auf dieselbe Weise verhalten, z. B. die Kranzblutadern des Herzens sich in die linke Vorkammer, eine oder mehrere Lungenvenen in die Hohlvene einsenken, eine grosse uberzahlige Lungenpulsader von der abstiegenden Aorta entsprang u.s.w., nur weitere Entwicklungen dieses Typus sind, und 3. die wichtige Bemerkung, class cliese Anastomosen in den Fallen, wo die Lungenpulsader verschlossen oder betrachtlich verengt war, und dennoch das Leben bedeutend hoch gebracht wurde, hochst warhscheinlich die Wege sind, clurch deren Erweiterung das Blut in die Lungenpulsadern geftihrt wurde. In der That werclen auch unter dieser Bedingung die Luftrohrenaste erweitert gefunden.
Many other authors, among them Hyrtl (5), Gegenbauer (6), Krause (7), Winslow (8), Bohmer (9), M. J. Weber (10), Arnold (11), and W. Gruber (12) note connections between the veins of the pulmonary and systemic circulations and describe them as anomalies or variations. Zuckerkandl (3) was the first to undertake the study of these problems. In a careful and masterly paper he both added to our knowledge of the pulmono-systemic anastomoses and attempted to account for and interpret the origin of the system as a whole by reasoning from his findings in the infant and adult. His work was carried out for the most part on the bodies of children which had been injected through the pulmonary vein with a thin colored injection mass. He found that the mass fills not only the pulmonary veins, but also the bronchial veins and through them the azygos, hemiazygos and mediastinal network of veins and in many cases reaches even the postcava and the gastric veins. The anastomoses between the pulmonary and sys PULMONARY VEIN IN THE DOMESTIC CAT 301 temic veins vary in size in different individuals, and within small limits vary in position, but the pulmonary veins regularly anastomose with the veins of the mediastinal network. He concludes, therefore, that the anomalies cited are caused by a local overgrowth of a capillary plexus in one position with a corresponding underdevelopment at the point where the vein in question should normally develop. In this manner he reasons that probably the pulmonary and systemic veins are merely remnants of an originally great indifferent plexus of capillaries from which lines of drainage have been developed as best suited to the functions of the part. Subsequent to the work of Zuckerkandl attention appears to have been confined mainly to the consideration of the pulmonaiy vein itself, and especially to the relation of its opening into the heart in the various stages of its development. Boas (13), Goette (14), and Hochstetter (15) describe the opening of the pulmonary vein into the auricle in the dipnoean, amphibian and reptile. Boas divides the sinus venosus into two portions. The left, which is the smaller receives the opening of the pulmonary vein. How it subsequently reaches its final position in the left auricle he does not definitely demonstrate. Goette considers that the vein first grows out from the sinus venosus, is then cut off from this and finally establishes its definitive orifice in the left auricle. Hochstetter merely states that the pulmonary vein opens first into the sinus venosus and subsequently in the left auricle. Schmidt (16) studies the opening of the pulmonary vein in the pig embryo.
In the embryo of 7 mm. he describes the vein as passing ventrally through the dorsal mesocardium to empty into the left portion of the sinus venosus, which is situated to the left of the common opening of the pre- and postcardinal veins. He then describes the absorption of the proximal segment of the vein into the auricular wall with the subsequent inclusion of its tributaries until four separate pulmonary veins empty into the auricle. The description of the opening of the vein in the left portion of the sinus venosus in the pig at this stage agrees with the conditions found in the cat embryo of a slightly earlier stage, that is, 5 to 6 mm. His (17) demonstrates the pulmonary vein as opening into the left portion of the sinus venosus in an early stage in the human embryo. The opening is situated to the left of the left valve of the sinus. The shift of position of the opening to its definitive site is the result of the progression of this valve to the left to join the lower portion of the septum superius on the posterior wall of the auricle. Born (18), Rose (19), and Narath (20) describe the vein as opening into the auricle but do not consider the early stages in detail. Flint (20) devotes the major part of his attention to the pulmonary arteries and bronchi and mentions the pulmonary vein only in passing. In the 5 mm. pig embryo he notes the presence of a plexus around the esophagus and describes the pulmonaiy vein as growing out from the sinus venosus. He states that from the sinus it passes dorsad in the dorsal mesocardium to the pulmonary anlage which at this stage is only partially separated from the esophagus. The venous radicles anastomose with the capillary plexus around the esophagus and pulmonary anlage thus forming a direct line of communication which leads from the ventral aspect of the pulmonary anlage to the dorsal wall of the sinus venosus. He makes no attempt to define the limitations of the plexus which he notes around the esophagus and consequently fails to recognize that it is only a part of a rich plexus which is present throughout the entire length of the gut and communicates freely with the adjacent systemic veins thus serving as a groundwork for future drainage lines between the respiratory and systemic circulations. His statement that the pulmonary vein grows out from the sinus venosus is not substantiated by any detailed evidence, nor does he explain the method by which this vein joins with the plexus around the pulmonary anlage. Fedorow (22) describes the development of the pulmonary vein in the amphibian, reptile, bird and mammal and concludes that the vein is an outgrowth of the dorsal wall of the sinus venosus at a point situated to the left of and above the opening of the cornua of the sinus. This opinion he bases on the fact that in the posterior wall of the sinus, not far from the auricle, he observed a proliferation of endothelium which projects into the dorsal mesocardium. Into this the cavity of the sinus tunnels and forms a single trunk which, a short distance from the sinus, gives off branches. These at a later stage, join with the capillaries of the pulmonary anlage and thus complete the pulmonary vein.
The subsequent behavior of the venous opening he describes as follows: 1. Der Teil des Sinus venosus, in den die Lungenvene einmundet, wird infolge des ungleichen Wachstums verschiedener Abschnitte der Herzwand in die Vorkammerwand mit aufgenommen. Auf diese Weise fliesst jetzt die Vene in den gemeinsamen Teil der Vorkammer ein, d.h. mehr kranial als sie friiher einmiindete. 2. Die weite Sinusmiindung verengt sich, indem eine besondere Falte der Herzwand an der Grenze zwischen dem Sinus und der linken Vorkammer von links nach rechts riickend nach innen einwachst ; diese Falte nenne ich den "Vorkammerboden." Die Venenmiindung bleibt dabei kranial vom Vorkammerboden liegen. 3. Indem die Vorkammerscheidewand allmahlich hoher wird und mit ihrer Insertion einenimmergrosseren Teil der Vorkammerwand einnimmt, erreicht sie die Venenmiindung und lasst friiher oder spater dieselbe links von sich liegen; claim wachst die Seheidewand mit dem Vorkammerboden zusammen und die Venenmiindung wird jetzt der linken Vorkammer gehoren. The above description of the course of the orifice of the vein as it passes to its definitive position in the left auricle immediately raises the question whether the 'Vorkammerboden' which he describes is other than the left valve of the sinus venosus. If it is the left valve of the sinus his description of its shift to the left to fuse with the lower portion of the septum superius corresponds with that of His. v. Mollendorf (23) disagrees with the findings of Goette and Fedorow as to the sprouting of the pulmonary vein from the sinus venosus. He considers that the vein is connected from the first with the capillary plexus around the pulmonary anlage and with the sinus venosus. He does not concern himself with the formation of the final opening of the vein into the left auricle, nor does he recognize the connection of the capillaries around the pulmonary anlage with those of the surrounding systemic vascular system. He further differs from all other observers in that he states that from the first there are two pulmonary veins which empty into the sinus venosus by separate orifices. From the foregoing review of the literature it will be seen that our knowledge of the morphology of the pulmonary vein is incomplete in two main points, namely, (1) The anlage of the vein and its connection with the sinus venosus has not been described in detail ; and (2) the method by which the vein changes its orifice in the center of the sinus venosus for one in that portion of the sinus which lies to the left of the left sinus valve has not been considered. In addition, the general relation which the pulmonary venous system bears to the systemic has been entirely neglected in the study of the embryology of the vein. It is the purpose of the present paper to follow the development of the pulmonary vein of the domestic cat from the early stage in which it empties into the cephalic portion of the sinus venosus in the median line to the stage in which it attains its definitive connection with the left auricle. At the same time, its relation to the systemic circulation will be considered from the standpoint of the drainage lines which exist normally in the infant and adult as shown by Zuckerkandl, enlargement of which gives rise to the so-called anomalies.
The material used in this investigation consisted of embryos of the domestic cat in the embryological collection of the Department of Anatomy of Columbia University. These were imbedded in paraffin, for the most part sectioned at 13.32^ and stained with hematoxylin (Delafield) and Orange G after the method of Morris (24). A few of the smaller embryos were stained in toto with borax carmine before being imbedded and sectioned.
The embryos studied ranged in size from 4.5 mm. to 7 mm. When deemed necessary reconstructions were made by the method of Born. The complete list of embryos studied is as follows : Nos. 82, 93, 134, 469, 4.5 mm. in length. No. 226, 5 mm. in length. Nos. 103, 110, 5.5 mm. in length. Nos. 84, 85, 109, 115, 116, 117, 128, 187, 283, 481, 482, 6 mm. in length. Nos. 129, 130, 131, 186, 261, 6.5 mm. in length. Nos. 105, 108, 119, 121, 135, 137, 138, 266, 281, 487, 488, 7 mm. in length. In addition, the process of development as outlined below has been substantiated by observation made upon the embryos of the chick in the Columbia collection, and the presence of the plexus around the esophagus and pulmonary anlage and its connection with the surrounding systemic veins has been observed by A. M. Miller 2 in connection with the developing blood cells in the mesenchyme of the chick.
- Personal communication.
The development of the vein, so far as it will be considered in this paper, may be divided conveniently into three stages according to the point of entrance of the vein into the venous portion of the heart, namely, (1) a stage in which the vein empties into the cephalic portion of the sinus venosus in the median line, (2) in which it empties into the sinus venosus to the left of the left sinus valve, and (3) in which it empties into the left auricle. 1,
First stage: embryos of 1.5 mm. (figs. 1 and 2) The heart consists of a single tube so twisted upon itself that the ventricular portion lies ventrad and caudad and the auricular portion dorsad and cephalad. At the dorso-cephalic extremity of the auricle the ducts of Cuvier unite to form the sinus venosus. Dorsal to and at a level slightly cephalad of the sinus venosus, the tracheal furrow on the ventral aspect of the gut ends in a slight dilatation, the pulmonary anlage. In the mesenchyme surrounding the intestinal tract throughout its entire length are many capillaries. For the most part these have formed a netlike plexus which anastomoses freely with the adjacent veins of the systemic circulation. In some places the plexus is incomplete and is represented by unconnected venous spaces, the anlages of capillaries. The anastomoses with the surrounding veins may be divided into cephalic and caudal groups; the cephalic group communicates with the capillaries around the aorta and with the precardinal and segmental veins and the caudal with the omphalo-mesenteric and postcardinal veins. The irregular network already shows a tendency to the formation of longitudinal drainage lines along the lateral and dorsal aspects of the intestine. The plexus will be designated the 'splanchnic plexus' (fig. 1, 10). In addition to the communications with the systemic veins noted above, the splanchnic plexus exhibits two well defined connections with the venous portion of the heart, (1) the cephalic or pulmonary, and (2) the caudal or postcaval. These are constant both in occurrence and position. 1. The pulmonary tap. In the region of the tracheal furrow the plexus is pushed forward by the projection of the furrow from the remainder of the intestinal tube. At its caudal extremity the plexus is very abundant, forms a network surrounding the pulmonary anlage and on the sides of the anlage the capillaries show a tendency to coalesce to form a longitudinal vein. At the ventral pole of the lung bud a common stem formed by the fusion of the capillaries of the two sides passes ventrad and slightly caudad through the dorsal mesocardium to open by a rounded orifice into the cephalic aspect of the sinus venosus in the median line, at a level cephalad of and between the ducts of Cuvier. 2. The postcaval tap. This is found caudal to the pulmonary anlage at the level at which the sinusoids of the liver are forming. It (figs. 1 and 2, 13) is formed by the junction of radicles of the lateral longitudinal lines of the splanchnic plexus which join in the median line at the cephalic limit of the liver, fuse into a single vessel which passes cephalad through the dorsal mesocardium and enters the caudal portion of the sinus venosus in the median line between the omphalo-mesenteric veins at a point opposite the opening of the vein from the pulmonary anlage. The caudal and cephalic taps are connected along the sides of the esophagus by the lateral longitudinal drainage lines before-mentioned. At this stage the pulmonary vein exists as a single vessel having two main vascular connections, namely, (1) ventrally a single rounded orifice in the sinus venosus, and (2), dorsally a connection with that portion of the splanchnic plexus which is pushed forward by the growing pulmonary anlage, which it joins at the ventral pole of the lung bud. If the possible routes of blood flow from the pulmonary anlage be considered it will readily be seen that aside from the main channel through which the blood is returned to the heart, there exist many subsidiary paths by which the blood may reach the systemic circulation. The connections with the pre- and postcardinal veins are the most important of these as they map out the future channels to the hemiazygos and azygos veins and thus in the adult form the bronchial veins. This rich plexiform network of the splanchnic plexus with its abundant inosculation with surrounding vessels explains the various anomalies of the pulmonary veins heretofore described, and explains also the normal communications which, as pointed out by Zuckerkandl, exist between the pulmonary, systemic and portal systems. In fact, the presence of this plexus with its communications with the heart through the pulmonary vein and with the systemic and portal systems through its connection with surrounding mediastinal veins fulfils the requirements of Zuckerkandl, who states: Dieser Anastomosencomplex der Lungenvenen wiirde sich leicht erklaren, wenn bekannt ware, welcher Art das Gefass-system der primaren Anlage ist und wie .sich aus demselben das respiratorisehe Netz entwickelt. Leider ist die Entwicklungsgeschichte noch nicht im Stande, hierauf eine geniigende Ant wort zu geben XJber das Verhalten der Blutgefasse zur primaren Anlage der Lunge, so wie auch uber die Entwicklung der Lungenvenen, desgleichen daruber, wie sich diese verschiedenen Gefassbezirke einers'eits zu einander stellen und andererseits ob und in welcher Weise die theilweise Ruckbildung der primaren Gefassen erfolgt, liegen keine bestimmten Untersuchungen vor. Bei genauerer Kenntniss der Entwicklungsgeschichte wird sich wahrscheinlich ergeben, dass die Verbindungen der Lungengefasse mit den bronchialen und mediastinalen, insbesondere aber die der letzteren bloss Reste von reichlichen Anastomosen sind, die vorher zwischen Lungen- und Korpervenen bestanden haben. Wenn dem so ist, wenn die Verbindungen Rest von reichlichen Anastomosen sind, so ist die Variabilitat in Bezug auf Localitat und Starke der Anastomosen leicht erklart.
Second stage: embryos of 5 to 6 mm. (figs. 3 and 4) The most important change from the preceding stage is noted in the shift in position of the sinus venosus in its relation to the auricle. The sinus has moved caudad and to the right and now empties into the caudal and right portion of the still undivided auricle. The right duct of Cuvier (fig. 4, 7) is very short and extends dorso-ventrally to empty into the right cornu of the sinus which is situated furthest to the right. The left duct of Cuvier (fig. 4, 8) formed by the junction of the left pre- and postcardinal veins, curves caudally and to the right to empty into the left cornu which then passes horizontally to the right and joins the caudal and left portion of the right cornu. The two cornua then open into the sinus by a common orifice (fig. 4, 9). The right limit of the sinus is well defined by a reduplication of the myocardium which projects ventrad and mesad into the cavity of the auricle as a vertical fold having a ventral free margin. This fold forms the right sinus valve. It is triangular in shape with the apex of the triangle directed upward and forward and continuous on the roof of the auricle with the septum spurium. The dorsal and caudal edges are continuous with the dorsal and caudal walls of the auricle. The left limit of the sinus venosus is hard to define as it shades gradually into the wall of the auricle. The left margin of the common opening of the cornua presents a very slight reduplication of the myocardium ventrad, the anlage of the left sinus valve. On the roof of the auricle in the median line the septum superius projects downward presenting a free edge below. The dorsal limit of this septum blends with the dorsal wall of the auricle at a point to the left of and cephalad to the upper limit of the left valve of the sinus. Between the left valve of the sinus and the septum superius at a level caudal to the dorsal limit of the latter is the opening of the cephalic tap of the splanchnic plexus, the pulmonary vein. This is situated just to the right of the median line (fig. 4, 11). The caudal tap of the splanchnic plexus enters the caudal aspect of the right cornu of the sinus on the left side just previous to its junction with the left cornu.
The pulmonary anlage (fig. 3, 2a) is represented by a retort shaped prolongation arising from the ventral aspect of the gut at the level of the upper limit of the auricle . This extends caudad and slightly ventrad to the level of the sinus venosus. Along either side of this tube is a plexus of capillaries which at the ventral pole of the anlage forms a definite vein which passes ventrad through the dorsal mesocardium. Just dorsalto the sinus venosus (fig. 3, 11), the two veins join to form a common trunk which after a short ventrad course meets the dorsal wall of the sinus venosus and passes through it as a long funnel shaped tap to empty by the orifice described above. Cephalad the pulmonary plexus communicates with the lateral longitudinal line of the splanchnic plexus on either side. The caudal tap (fig. 3, 12) has become a well marked vein which passes cephalad just to the right of the median line to the level of the lower limit of the sinus venosus. At this point it bends sharply to the right and passes through the dorsal mesocardium behind the dorsal wall of the sinus venosus to empt}^ into the left caudal aspect of the right cornu of the sinus as described above. The connection of this vein dorsally with the left longitudinal line of the splanchnic plexus is represented only by a capillary plexus which communicates freely with the sinusoids of the liver Above the level of the upper surface of the liver, between it and the pulmonary plexus the lateral lines of the splanchnic plexus form a plexus surrounding the esophagus which communicates above with the pulmonary plexus and below with the sinusoids of the liver and through these with the postcaval tap. On the right side the caudal tap of the plexus is well formed below the level of its orifice into the sinus venosus and can now be recognized as the anlage of the hepatic and suprahepatic portions of the postcava. From the above it is clear that the change in relation of the orifices of the veins opening into the sinus venosus is the result of unequal growth in the various portions of the sinus. The opening of the pulmonary vein has followed the caudal progression of the sinus and as the growth of the two sides has been equal at this level the orifice retains its original median position in the sinus. Caudal to this level growth has been markedly unequal on the two sides, the left increasing in width much more rapidly than the right. As a result, the lower portion of the sinus has shifted to the right side and now opens into the caudal and right aspect of the auricle. The evidence going to prove this inequality of growth is two-fold, (1) The left duct of Cuvier and the left cornu of the sinus are long drawn out and pursue a lateral course from above downward and from left to right, while the right duct of Cuvier and the right cornu are short and pursue a dorso- ventral direction; (2) The caudal tap of the splanchnic plexus ascends in the dorsal mesocardium to the level of the lower limit of the sinus venosus, then bends sharply to the right and pursues a horizontal course behind the sinus until it reaches its entrance into the right cornu just before the fusion of the latter with the left to form a common orifice. Referring to the previous stage, the relative position of the orifice into the sinus has changed but little, the point of entrance still representing the original median line of the sinus which has disappeared through the fusion of the two cornua. The horizontal course through the dorsal mesocardium behind the sinus represents the amount of growth of the left portion of the auricular wall over that of the right . The plexus around the pulmonary anlage still retains its lines of venous drainage, the pulmonary vein draining into the systemic circulation by means of the connections of the pulmonary plexus with the cephalic portions of the lateral longitudinal lines. Below the pulmonary plexus communicates with the caudal tap by means of the esophageal plexus which represents the lateral and posterior longitudinal lines of the splanchnic plexus. In addition to these communications the well known broncho-pulmonary anastomoses in the lung bud itself are easily recognized. Third stage: Embryos of 6.5 to 7 mm. (figs. 5 and 6) The sinus venosus with the exception of the openings of the cornua has been incorporated into the auricle. The right valve of the sinus (fig. 6, 40) is very prominent and above is continued into the septum spurmm which has shifted to the left and fused with the septum superius. The left valve of the sinus has likewise shifted to the left and its cephalic extremity on the dorsal wall of the auricle has fused with the dorso-caudal portion of the septum superius. As a result of the latter shift the orifice of the pulmonary vein has preceded the left valve of the sinus, passed under the septum superius, and now empties into the left auricle having both septum superius and left Valve of the sinus, or in other words, the interauricular septum on its right (fig. 6, 11). The pulmonary anlage shows a division into two lateral tubular prolongations, the anlages of the bronchi, which are surrounded by a rich capillary plexus. From the ventro-caudal aspect of each of these plexuses a well marked channel passes caudo-ventrally to unite with its fellow of the opposite side, and, after a very short course in the dorsal mesocardium, enters the wall of the left auricle, passes through it by a long funnel shaped tap and empties into the auricle by the orifice described above. From the dorso- cephalic portion of the pulmonary plexus of either side small vessels extend cephalad and dorsad to empty into the lateral longitudinal lines of the splanchnic plexus, thus mapping out the course of the future bronchial veins to the azygos and hemiazygos veins. The caudal tap of the splanchnic plexus is now a well marked vein which lies on the right side of the median line, receives the hepatic sinusoids and is plainly recognizable as the pars hepatica and suprahepatica of the postcava. The paths of communication between the pulmonary plexus above and caudal tap of the plexus below remain as many small anastomoses between the pulmonary capillaries above with the adjacent systemic veins and the communications of the latter with the postcaval tap below the septum transversum. The broncho-pulmonary anastomoses in the lung bud itself are still present. The orifice of the pulmonary vein has now, by the fusion of the left sinus valve with the septum superius, been transferred to the left auricle. The two subsidiary lines of drainage described in the previous stages are retained, but in markedly different degrees. That from the pulmonaiy plexus to the cephalic portion of the lateral longitudinal lines consists of several well marked channels which map out the future course of the bronchial veins. The caudal line of drainage to the postcava exists now only as small capillary anastomoses between pulmonary plexus on the one hand and the esophageal and aortic plexuses on the other, thus accounting for the irregularity of the connections between pulmonary and mediastinal veins and through the latter with the portal and postcaval systems described by Zuckerkandl. Summary. It is thus seen that the common pulmonary vein develops from the cephalic communication between the splanchnic plexus and the sinus venosus. The plexus is pushed forward by the developing lung bud and is carried ventrad and caudad as the pulmonary anlage develops. With the displacement of the sinus venosus caudad and to the right due to the inequality of growth of the two halves of the sinus and auricle, the pulmonary orifice moves only slightly to the right and empties into the left portion of the sinus, to the left of the left sinus valve and at a level below the septum superius. The formation of the interauricular septum by fusion of the left sinus valve with the dorsocaudal extremity of the septum superius definitely assigns the pulmonary vein to the left auricle. The plexus around the lung bud is differentiated into two systems, (1) from its ventral and caudal portion, the pulmonary for the fulfillment of the respiratory function, and (2) from the caudal and cephalic portion the bronchial for the venous drainage of the lung tissue proper. This is diametrically opposed to the opinion of Fedorow who states that he cannot accept the view of an originally indifferent plexus of capillaries which may develop on the one hand into veins and on the other inosculate with arteries, but believes that the vein grows directly from the dorsal wall of the sinus venosus as a bud finally to inosculate, after dividing into countless branches, with the plexus around the pulmonary anlage. while the artery approaches the opposite extremity of the plexus growing in a similar manner from the sixth aortic arch. That portion of the splanchnic plexus lying between the pulmonary anlage cephalad and the hepatic sinusoids caudad serves as a temporary direct communication between the pulmonary vessels and the systemic circulation represented by the postcaval tap of the splanchnic plexus. The paths by which this circulation is carried out have already been described. With the further development of the pulmonary veins this portion of the splanchnic plexus loses its connection with the pulmonary capillaries m except for the persistence of occasional small veins which pass from the pulmonary capillaries to the esophageal or aortic plexuses, thus mapping out the communication of the pulmonary veins with the postcaval and portal systems through the veins of the posterior mediastinum. This conception of the pulmonary system, namely, that it is simply a specially developed part of an indifferent plexus originally present in this region, assigns to the vein its proper position in the general vascular complex. It also serves to explain the small communications between pulmonic and systemic circulations normally present in the adult and the large channels occasionally found which are classed as anomalies of the pulmonary veins. An anomaly of the right pulmonary vein A specimen of most unusual abnormality of the right pulmonary vein which bears out the conception of the development of the pulmonary system as given above was presented to the Anatomical Department of Columbia University by Dr. Edwards A. Park. Although previously published (25) with a short and incomplete note as to the probable etiology of the anomaly, a brief description will be given here. On ventral view (fig. 7) the heart was normal save for a small teat-like process attached to the tip of the left auricular appendage. The dorsal view (fig. 8) showed complete absence of any right pulmonary vein entering the left auricle. The right lungwas very small and compressed -against the inner wall of the thorax by the heart which in turn was pushed to the left by a very large left lung. In the main interlobar fissure of the right lung was a good sized venous channel, the pulmonary vein which, beginning in the region of the hilum ran caudad to the diaphragm, pierced it, and on reaching its abdominal surface turned sharply to the left to enter the right aspect of the postcava in its course between liver and diaphragm (fig. 9). The vein in this instance is a persistence, on the right side, of the lateral line of communication between the cephalic and caudal taps of the splanchnic plexus (fig. 3, 14) accompanied by a loss of 'the normal communication between the plexus on the right side of the pulmonary anlage and the common stem of the pulmonary vein. The anomaly is unusual because of the entire absence of the normal entrance of the right pulmonary vein into the left auricle, the entrance of the pulmonary vein into the postcava representing merely the enlargement of a very small channel which is frequently present in the adult mammal.
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Explanation of Figure 1
Schema of the left side of a wax reconstruction of a 4.5 mm. cat embryo. Columbia collection no. 134, X 200. The left cornu of the sinus venosus together with the structures entering it, has been removed. 2, gut 2a, pulmonary anlage 4, left postcardinal vein 6, left precardinal vein 8, left duct of Cuvier 9, sinus venosus 10, splanchnic plexus 11, cephalic tap of the splanchnic plexus into the cephalo-mesial portion of the sinus venosus (common pulmonary vein) 12, communications between splanchnic plexus and precardinal vein caudal tap of splanchnic plexus (hepatic portion of postcava) communications between the splanchnic plexus and postcardinal vein 13 U The engravings in this paper were supplied by the author. 316 PULMONARY VEIN IN
ExPLAXATIOX OF FlGURE 2
Composite drawing of super bryo, Columbia collection no. 134, reduced; schematic. 1, aorta 2, gut 2a, pulmonary anlage 3, right postcardinal vein 4, left postcardinal vein 5, right precardinal vein 6, left precardinal vein 7, right duct of Cuvier 8, left duct of Cuvier 9, sinus venosus 10, splanchnic plexus imposed cross sections of the 4.5 mm. emin the region of the cervical bend, X 150, 11, cephalic tap of splanchnic plexus 1 common pulmonary vein I 1-j. caudal tap of splanchnic plexus (hepatic portion of postcava) 15, neural tube 16, coelom 17, right umbilical vein 18, left umbilical vein 19, right omphalo-mesehteric vein 20, left omphalo-mesenteric vein 32, liver
Explanation of Figure 3
Right side of a wax reconstruction of the 5.18 nun collection, no. 226, X 150, reduced. 1, aorta 2, gut 2a, pulmonary anlage 3, right postcardinal vein 5, right precardinal vein 9, sinus venosus 10, splanchnic plexus 11, pulmonary vein embryo, Columbia 12, caudal tap of splanchnic plexus (hepatic portion of postcava) 14, remnants of former communication between the thoracic and abdominal portions of the splanchnic plexus 21, conus arteriosus 22, common ventricle
Explanation of Figure 4
Wax reconstruction of the 5.18 mm. embryo, Columbia collection, no. 226, X 150, reduced. Viewed from above, the top of the common auricle having been removed. 1, aorta 2, gut 2d, pulmonary anlage 4, left postcardinal vein 7, right duct of Cuvier 8, left duct of Cuvier 9, common opening of the cornua into the sinus 10, component parts of the splanchnic plexus 11, pulmonary vein 21, conus arteriosus 23, common auricle 38, auriculo-ventricular orifice
Explanation of Figure 5
Wax reconstruction of the heart of the 7 mm. embryo, Columbia collection, no. 266, X 75, reduced. Viewed from behind showing the crossing of the left duct of Cuvier to the right consequent to the shift of the sinus venosus. 2a, pulmonary anlage 9, right cornu of the sinus venosus 3, right postcardinal vein 11, pulmonary vein 4, left postcardinal vein 13, caudal tap of the splanchnic plexus 5, right precardinal vein (hepatic portion of postcava) 6, left precardinal vein 22, common ventricle 7, right duct of Cuvier 26, right auricle 8, left cornu of the sinus venosus 27, left auricle
EXPLANATION OF FIGURE 6
Wax reconstruction of the 7 mm. embryo, Columbia collection, no. 266, X 75, reduced. Viewed from above, the top of the auricles having been removed. 22, common ventricle 26, primitive right auricle 27, primitive left auricle 38, auriculo-ventricular orifice 39, right valve of the sinus venosus 40, anlage of the interauricular septum /, aorta 2a, pulmonary anlage 8, left cornu of the sinus venosus 9, sinus venosus 11, pulmonary vein 21, conus arteriosus
Explanation of Figure 7
Ventral view of congenitally abnormal heart. 24, right ventricle 34, arch of the aorta 25, left ventricle 35, innominate artery 26, right auricle 36, left common carotid artery 27, left auricle 37, left subclavian artery 29, left pulmonary vein 46, precava 81, left pulmonary artery 8 Dorsal view of congenitally abnormal heart. 24, right ventricle 25, left ventricle 26, right auricle 27, left auricle 29, left pulmonary vein 30, right pulmonary artery 31, left pulmonary artery 33, azygos communis vein 34, arch of aorta 35, innominate artery 36, left common carotid artery 37, left subclavian artery 46, precava 47, postcava 9 Schema of abnormal pulmonary has been removed. 28, right pulmonary vein 29, left pulmonary vein 30, right pulmonary artery 31, left pulmonary artery 34, arch of aorta circulation, ventral view. The heart 41, right inferior phrenic artery 44, right lung 45, left lung 46, precava 47, postcava
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