DEVELOPMENT' OF THE VEINS IN THE EMBRYO IMC. 27 



cardinal veins making that part of the vena cava which is opposite- the renal veins in the 

 adult; none of the posterior cardinal veins persists. Below the level of the renal veins the 

 vena cava arises from the right prevertebral caval plexus. It connects freely with the 

 veins of the Wolttian bodies as long as these organs persist. It thus becomes clear that 

 the entire prevertehral plexus is an important structure. In the thoracic region the a/ygos 

 system develops in the more medial part of the plexus, dorso-lateral to the aorta; in the 

 lower abdominal region, the third segment of the inferior vena cava and the ascending 

 lumbar veins develop from the more lateral part of the plexus, so that these veins must be 

 considered as arising as longitudinal trunks of the same plexus. Thus a view of the 

 prevertebral veins (such as is given in figure 495 of the Spalteholz Handatlas der Anatomic, 

 Bd. II, Auflage 7, 1913) has this significance, that all of the prevertebral veins shown 

 there, the azygos system, the ascending lumbar veins, and the inferior segment of the 

 vena cava, have a common origin. The origin of the inferior vena cava, from the mesial 

 cardinal veins and the prevertebral plexus, explains the well-known anastomoses of the 

 vena cava in the adult. 



No vein has a more extensive or a more interesting literature than the inferior vena 

 cava. Our present ideas in regard to the vena cava may be said to begin with the work of 

 Rathke, and the prevailing theory of the origin of the lower segment of the vein is the 

 theory of Hochstetter. In 1830 Rathke discovered the fact that the lower segment of the 

 inferior vena cava is double and symmetrical in the embryo. This was published in the 

 Merckel's Archiv for 1830. In the same year he stated that the lower part of the inferior 

 vena cava came from the right cardinal vein. His own words, as quoted by Kerschner, are: 

 "Die Vene der rechten falschen Xiere ist die nachherige hintere (untere) Hohlvene, die der 

 linken die nachherige Vena hemiazyga." This view of the inferior vena cava is the same 

 as that of Hochstetter. Rathke, however, in his subsequent work, published in 1838, gave 

 up the theory that the lower segment of the inferior vena cava came from the posterior 

 cardinal vein, because he had specimens in which two vessels were present, namely, a 

 vessel medial to the kidney, making the anlage of the vena cava, and a vessel lateral to 

 the kidney or the posterior cardinal vein (see Kerschner, p. 812). This is the condition 

 shown in the diagram of figure 14. Notwithstanding this observation of Rathke, the work 

 of Hochstetter (1893) has been practically universally accepted. Hochstetter studied the 

 development of the entire vena cava in the rabbit. He described the development of the 

 vena cava in the liver and based the study of the relation of the cardinal system to the 

 liver veins on the work of Goette. It has already been noted that F. T. Lewis has cleared 

 up this part of the subject by showing that it is the mesial cardinal or subcardinal vein 

 which makes the connection with the liver. Hochstetter then developed the theory that 

 the lower segment of the inferior vena cava is a transformed posterior cardinal vein. As 

 can be seen in his figures, especially in his figure 19, Taf. 22, 1893, Hoehstetter's view is 

 merely a different interpretation of the same observations, for, in the same specimen, he 

 shows both an inferior vena cava mesial to the kidney and a posterior cardinal vein lateral 

 to the kidney. 



In 1888 Kerschner analyzed the views of Rathke and Hochstetter and concluded that 

 the lower segment of the inferior vena cava could not be a transformed posterior cardinal 

 vein for two reasons: first, the vena cava has a position more mesial and more ventral than 

 the posterior cardinal ever has; and secondly, at a certain stage both veins are present in 

 the same specimen. This sums up the whole question, the facts being that the lower seg- 

 ment of the inferior vena cava is at first double and comes from the bilateral prevertebral 

 plexus and that this new pathway takes the place of the posterior cardinal system which 



