1 68 ELEMENTS OF MAMMALIAN ANATOMY 



spinal cord in the region of the atlas, and after making a strong 

 anastomosis with the internal jugular vein, descends in com- 

 pany with the vertebral artery through the transverse foramina 

 canal of the first, six cervical vertebrae. The left vertebral vein 

 is a tributary of the left innominate (Fig. 84). 



The imiominate vein is formed by the union of the subclavian 

 and the external jugular. Sometimes the vertebral vein joins 

 also in the union instead of emptying into the superior vena cava. 

 The subclavian vein returns the blood from the arm and accom- 

 panies the subclavian artery. The external jugular veins are 

 large vessels lying on either side of the neck beneath the platys- 

 ma myoids muscle. When the skin is removed, the veins are 

 plainly seen through this very thin muscle. The external jugu- 

 lar is formed ventral to the angle of the mandible by the union 

 of the anterior and posterior facial veins. The anterior facial 

 are united by a large transverse vein. The two tributaries of 

 the external jugular are the transverse scapular vein and the 

 internal jugular. The former receives the cephalic vein, a 

 superficial vein on the lateral aspect of the arm, and the latter 

 is the small vein returning from the brain. 



A system of tube-like spaces, called sinuses, whose walls are 

 formed by the dura mater lined with epithelium, takes the 

 place of the large venous trunks within the cranial cavity. 

 These sinuses are usually not filled by a starch injection, but 

 may be filled by a gelatin mass. They cannot be dissected by 

 the beginner. The superior longitudinal sinus extends in the 

 median line beneath the roof of the skull, from the ethmoid 

 region to the tentorium cerebelli, where it bifurcates to form the 

 lateral sinuses, which proceed laterad and ventrad in the sub- 

 stance of the tentorium. The lateral sinus emerges from the 

 tentorium just caudad to the petrosal bone, where it follows 

 the groove to the jugular foramen. This groove may be seen 

 in a bisected or unroofed skull. 



The superior petrosal sinus lies in the angle formed by the 

 junction of the tentorium and the petrosal bone, and unites 



