234 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



it may be followed forward. As both have identical branches, it is necessary 

 to follow only one. The one whose branches appear to be filled with blood 

 should be selected; the left one is usually easier to follow. In specimens which 

 have been preserved for a long time the dissection of the branches of the precaval 

 veins is generally unsatisfactory because the branches are often empty, but, of 

 those named below, as many as the condition of the specimen permits should 

 be identified. Be very careful not to injure the adjacent arteries springing from 

 the ventricle. Trace the precaval forward out of the pericardial sac. Shortly 

 anterior to the place where the precaval penetrates the pericardial sac the vein 

 receives practically simultaneously four tributaries, three small and one large, 

 one. The most medial branch is the small thyreo-scapular vein which collects 

 a branch from the thyroid gland (the gland situated in the fork of the large 

 arteries) and then passes to the inner surface of the shoulder where it collects 

 from several muscles. Lateral to this vein is the slightly larger internal jugular 

 vein. This runs anteriorly along the side of the neck in contact with a white 

 nerve (vagus or tenth cranial nerve). It receives medially an extensive net- 

 work of branches from the esophagus. It may be traced anteriorly to the base 

 of the skull from which it issues, making an anastomosis with the external jugular 

 vein, soon to be described. The third tributary of the precaval vein is the large 

 subclavian vein, by far the largest of the four branches which enter the precaval. 

 It passes along the side of the neck and as the axillary vein turns toward the 

 shoulder. Here it is seen to be formed by the union of two large branches, 

 the external jugular vein from the neck and the brachial from the fore limb. The 

 external jugular lies along the side of the neck, lateral and dorsal to the internal 

 jugular. It collects from the head, and in its passage posteriorly along the neck 

 has at regular intervals vertebral veins passing into it from between the vertebrae. 

 Near its junction with the brachial it receives the last of the vertebral veins 

 which descends from the junction between last cervical and first trunk vertebra, 

 where it connects with the anterior end of the vertebral vein described with the 

 renal portal system. The external jugular vein also receives branches from the 

 skin and muscles of the shoulder region. The fourth and most lateral and dorsal 

 of the tributaries of the precaval is a small scapular vein which comes from the 

 muscles covering the scapula. 



Draw the branches of the precaval as far as you have found them. 



b) The left hepatic vein: The left hepatic vein should be traced into the left 

 lobe of the liver from which it collects venous blood. To do this, clear away the 

 intervening posterior wall of the pericardial sac and pleuroperitoneum. 



c) The postcaval vein: Trace the postcaval vein posteriorly into the right lobe 

 of the liver. Its course may be followed by making a slight hole in the vein 

 where it enters the sinus and probing posteriorly into the hole, dissecting away 

 the liver substance along the probe. Note the numerous hepatic veins which 

 enter the postcaval during its passage through the liver. Find where the post- 



