COMPARATIVE ANATOMY OF THE CIRCULATORY SYSTEM 255 



courses parallel to the preceding but dorsal to it and collects chiefly from the 

 latissimus dorsi muscle. There is a broad connection between the thoracodorsal 

 and subscapular veins. Lateral to these branches the axillary vein is known as 

 the brachial vein. It runs along the inner surface of the upper arm in company 

 with nerves and the brachial artery. These structures will be found by separat- 

 ing the muscles on this surface of the upper arm. 



Return now to the external jugular vein. It soons receives on its medial 

 side the very small internal jugular vein which passes forward in the neck along- 

 side the trachea in company with the carotid artery and vagus nerve. The 

 much larger external jugular vein assumes a more superficial position and in 

 addition to small branches from adjacent muscles receives the large transverse 

 scapular vein from the shoulder. This passes laterally in front of the shoulder 

 and anastomoses with the cephalic vein of the arm. The cephalic vein is the 

 superficial vein of the fore limb and will be found on the external or lateral 

 surface of the upper arm. It also connects with the posterior circumflex vein 

 described above. The external jugular anterior to the entrance of the transverse 

 scapular vein is situated in the sternomastoid muscle. On following it forward 

 it is seen to be formed at the angle of the jaw by the union of the anterior and 

 posterior facial veins. At their point of union they are connected across the 

 ventral side of the throat by the transverse vein which has probably been 

 destroyed. The anterior facial vein collects from the face and jaws and sub- 

 maxillary and lymph glands, its main tributary being the angular vein from the 

 region of the eye. The posterior facial vein emerges from the parotid gland and 

 at the place of emergence receives the posterior auricular vein from the pinna 

 and back of the head. The main vein then lies imbedded in the parotid gland and 

 may be followed by dissecting away the gland. It is then seen to be formed by 

 the union of veins from the temporal region and region anterior to the ear. 



Draw the branches of the precaval as far as found. 



b) The branches of the postcaval: The following description applies to both 

 the rabbit and the cat. Turn the apex of the heart forward and note the large 

 vein which enters the right auricle from behind. This is the postcaval vein 

 (also called vena cava posterior or inferior and ascending vena cava). It passes 

 posteriorly in the thorax, lying slightly to the right of the median line, inclosed 

 in the free dorsal border of the caval fold of the pleura. Follow it caudad. It 

 passes through the diaphragm from which it receives several phrenic veins. In 

 the rabbit it then lies against the dorsal wall of the peritoneal cavity slightly 

 to the right of the median line, dorsal to the right median lobe of the liver and 

 in contact with the hepatic portal vein. It then passes into the right lateral 

 lobe of the liver from which it emerges near the right kidney. In the cat the 

 postcaval vein passes into the right median lobe of the liver and inclosed in the 

 liver substance traverses the length of the liver emerging from the posterior 

 lobule of the right lateral lobe. Note the large hepatic veins which flow from the 



