7PS 



DEVELOPMENT OF THE VASCULAR SYSTEM. 



to left. The communicating branch between the primitive jugular veins is 

 converted into the left innominate vein. The portion of vessel between the 

 rio-ht subclavian vein and the tennination of the communicating branch becomes 



Fisr. 595. 



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, thep)arts 

 of the heart being removed or seen tlirougli. 



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 communi- 

 cating 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 tlie 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 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 coronaiy sinus. Even i^i 

 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 



