232 



VASCULAK SYSTEM 



The primitive jugular veins are at first symmetrical and join, as already stated, 

 the posterior cardinals to form the ducts of Cuvier. A communicating branch is, 

 however, formed between the point of junction of the left jugular and subclavian 

 veins and the right jugular. This anastomosing vessel is converted into the left 

 innominate vein. The portion of the right primitive jugular between the transverse 

 vessel and the right subclavian becomes the right innominate, while the portion 

 between it and the entrance of the posterior cardinal (vena azygos major), together 

 with the duct of Cuvier, forms the definitive superior vena cava. On the left side 

 the portion of the primitive jugular below the anastomosis becomes the superior 

 intercostal, but the duct of Cuvier becomes obliterated (with the exception of a 

 portion which in part forms the coronary sinus). Traces of the vessel are to be 

 recognised even in the adult, in the form of a fibrous strand which runs over the 



FIG. 290. A AND B. DIAGRAMMATIC OUTLINES OF THE VESTIGE OF THE LEFT SUPERIOR CAVA 

 AND OF A CASE OF ITS PERSISTENCE. (Sketched after Marshall.) 3. 



The views are supposed to be from before, the parts of the heart being removed or seen through. 



1, 1', internal jugular veins; 2, 2', subclavian veins; 3, right innominate; 3', right or regular 

 superior cava; 4, left innominate, normal in A, rudimentary in B; 5, in A, the opening 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; 6, coronary sinus; 6', coronary veins ; 7, superior 

 intercostal trunk of the left side (left cardinal vein) ; 8, the principal azygos (right cardinal vein) ; 

 7', 8', some of the upper intercostal veins ; 9, the opening of the inferior vena cava, with the Eustachiaii 

 valve. 



back of the left auricle, and a small vein (oblique vein of Marshall) ; and in front 

 of the root of the left lung there remains an indication of its former presence in the 

 form of a small fold of pericardium (vestigial fold of Marshall). 



The left duct of Cuvier has been observed persistent as a small vessel in the 

 adult. Less frequently a right and a left innominate vein open separately into the 

 right auricle, an arrangement which is also met with 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. 



Veins of the limbs. The veins of the limb -buds form, to begin with, a 

 vascular loop with two marginal vessels. Of these latter the ulnar and the fibular 

 are the primary stems. Each extends down the postaxial border of its proper limb 



