THE THORAX loil 



The extracranial part of the anterior cardinal vein, after the obUteration 

 of the vena capitis lateralis, commences at the jugular foramen, whence it 

 extends caudalwards, receiving in its course the cervical segtnental veins. In 

 the vicinity of the sinus venosus it meets the posterior cardinal vein of its 

 own side, with which it unites. The venous trunk thus formed is called 

 the duct ol Cuvier, of which they are two — right and left. These two ducts 

 pass transversely, one on either side, to the sinus venosus, into which they 

 open. At this stage the sinus venosus also receives the vitelline and um- 

 bilical veins of each side. The ducts of Cuvier form the primitive right and 

 left superior venae cavse. 



As the heart descends from the region of the fore-gut, the ducts of Cuvier 

 become vertical, and are in line with the anterior cardinal veins. When the 

 sinus venosus becomes merged into the right auricle, and the heart undergoes 

 a shght rotation from right to left, the left duct of Cuvier is placed dorsal to 

 the left auricle, before opening into the right auricle. 



Each anterior cardinal vein is joined, near its caudal extremity, by the 

 corresponding subclavian vein. 



Close to the junction the subclavian vein receives the external jugular 

 vein. This vein is a secondary formation, and is probably derived from a 

 posterior auricular vein, being subsequently reinforced by a pre-auricular 

 vein. 



A transverse anastomotic vessel is now formed, called the transverse 

 jugular vein. It extends from the junction of the left anterior cardinal and 

 left subclavian veins to the right anterior cardinal vein at a point a little 

 below the place where it receives the right subclavian vein. This transverse 

 jugular vein, which extends obliquely from left to right, with a downward 

 inclination, gives rise to the left innominate vein. The venous blood from 

 (i) the left side of the head and neck and (2) the left fore-hmb now passes 

 through the left innominate vein into the permanent superior vena cava. 

 The right innominate vein is formed by the short portion of the right anterior 

 cardinal vein which intervenes between the place where it receives the right 

 subclavian vein and the place where the transverse jugular vein joins it. 

 The portion of the right anterior cardinal vein, which lies immediately below 

 the place where the transverse jugular vein joins it, forms the upper or extra- 

 pericardial part of the permanent superior vena cava — that is to say, the 

 part above the point where the right azygos vein opens into it. The lower 

 or intrapericardial part of the superior vena cava is developed from the right 

 duct of Cuvier. The permanent superior vena cava therefore represents 

 (i) the lower part of the right anterior cardinal vein, and (2) the right duct 

 of Cuvier. 



The portion of the left anterior cardinal vein immediately below the left 

 extremity of the transverse jugular vein forms the upper part of the left 

 superior intercostal vein, thus accounting for the ending of that vein in the 

 left innominate vein, which, as stated, is formed by the transverse jugular 

 vein. 



The left duct of Cuvier undergoes partial obliteration. Its terminal part, 

 along with the left lateral comu of the sinus venosus, gives rise to the coronary 

 sinus. The portion next the terminal part also persists in the form of a very 

 minute vein, called the oblique vein of Marshall, which lies over the posterior 

 aspect of the left auricle. The obliterated portion is represented by the 

 vestigial fold of Marshall, which is contained within a small triangular fold 

 of the serous portion of the pericardium, in front of the root of the left lung. 



Posterior Cardinal Veins. — These are two in number — right and left — and 

 they return the blood from the Wolffian bodies, body-wall, and hind-hmbs. 

 They he on either side of the aorta, dorsal to the mesial part of the Wolffian 

 bodies. The caudal end of each vein receives the sciatic vein, which is the 

 primitive vein of the hind-Hmb. A little above this point it is joined, at a 

 later period, by the external iliac vein, which, along with the femoral vein, 

 has now been developed. 



The cephalic end of each posterior cardinal vein joins the corresponding 



