254 CIRCULATORY SYSTEM. 



sternal end of the clavicle, it is joined at the internal edge of 

 the scalenus anticus by the subclavian vein, and the union of 

 the two forms the vena innominata. 



The internal jugular receives frequently the large anastomotic 

 branch, just alluded to, from the external jugular, at the under 

 margin of the parotid gland, between the digastric muscle and 

 the lower jaw, and it is in this vicinage that it is generally re- 

 enforced by the Occipital; the Lingual; the Facial; the Pha- 

 ryngeal ; and the Superior Thyroidal Veins, that have been de- 

 scribed. 



The Vena Innominata, or Brachio Cephalic Vein, is the trunk 

 formed on either side by the junction of the subclavian with the 

 internal jugular. On the right side it looks like the continua- 

 tion of the internal jugular, and descends in contact with the 

 right pleura, behind the right side of the sternum, for the dis- 

 tance of an inch or thereabouts. On the left side it crosses be- 

 hind the superior end of the sternum, descending obliquely in 

 this course, from left to right, until it joins the trunk on the 

 right side. It lies in front of the great vessels proceeding from 

 the arch of the aorta; and is much longer than the trunk of the 

 other side. A common name for it is the Transverse Vein. 



The Vena Cava Superior, or Descendens, arises from the 

 junction of the two venae innominatae. It begins between the 

 cartilage of the first rib on the right side, and the arch of the 

 aorta, and descends to the superior posterior part of the right 

 auricle, into which it empties itself. Its course is not entirely 

 vertical, but inclining somewhat to the left side and forward. 

 It is about three inches long. The superior third of it is free, 

 and is in contact on the right with the pleura, and on the left 

 with the arteria innominata; the remaining portion of it is in- 

 vested by the pericardium, and has the aorta on its left anterior 

 face.* 



The following venous trunks discharge into the venae inno- 

 minatae, or into the descending cava. The Inferior Thyroidal; 

 the Vertebral; the Superior Intercostal; the Internal Mammary; 

 the Vena Azygos, and some others of smaller size. 



* In some very rare cases there have been two descending venx cavae, one for 

 the right side and the other for the left. J. F. Meckel. 



