622 THE BLOOD-VASCULAR SYSTEM OF THE OX 



surfaces of the digits and unite in the interdigital space to form a trunk which is a 

 satelUte of the volar common digital artery. 



The internal and external digital veins lie in front of the corresponding arteries. 

 They are connected with the volar digital vein by a large branch which passes 

 between the flexor tendons and the first phalanx. At the distal end of the meta- 

 carpus each inclines forward and anastomoses with the volar common digital vein 

 to form the volar venous arch. The inner vein is continued as the internal volar 

 metacarpal vein along the inner border of the suspensory ligament, and becomes a 

 satellite of the radial artery in the forearm, while the outer one is continued on the 

 jwsterior face of the metacarpal bone by two irregular veins, the external and 

 middle volar metacarpals. The latter anastomose freely with each other and 

 with the inner vein. They unite below the carpus or join the volar common 

 digital vein. 



The accessory cephalic vein is the upward continuation of the dorsal meta- 

 carpal vein and is much larger than in the horse. 



The posterior vena cava is partially embedded in the medial l^order of the 

 liver. Its abdominal part has a thicker wall than in the horse. Its affluents 

 correspond to the arteries of which they are satellites. The renal veins are large 

 and thick-walled; they run ol^liquely forward and join the vena cava at an acute 

 angle. The left one is much the longer. 



Two middle sacral veins usually accompany the artery. 



The veins of the mammary glands deserve special notice. They converge to 

 a venous circle at the l)ase of the udder, which is drained chiefly by two pairs of 

 veins. The subcutaneous abdominal vein (anterior mammary or ''milk" vein) 

 is very large in animals of the dairy breeds and its course along the ventral wall of 

 the abdomen is easily followed. It is usually flexuous. It emerges at the anterior 

 border of the udder about two or three inches (ca. 5 to 8 cm.) from the linea alba, 

 runs forward (deviating a little outward), dips under the panniculus, passes through 

 a'foramen in the abdominal wall about a handbreadth from the median plane, and 

 joins the internal thoracic vein. The external pudic vein (middle mammary vein) 

 is also of considerable size. It ascends in the inguinal canal as a satellite of the 

 artery and joins the external iliac vein. The right and left veins are connected at 

 the posterior border of the base of the udder by a large transverse branch. From 

 the latter arises the perineal vein (posterior mammary vein) , which runs medially 

 upward and backward to the perineum, turns around the ischial arch, and joins 

 the internal pudic vein. In the male these veins are relatively small. 



The deep veins of the thigh and leg resemble those of the horse, but there is no 

 recurrent tibial vein. 



The saphenous vein is much smaller than in the horse. 



The recurrent tarsal vein (external saphenous) is large. It is the upward 

 continuation of the external plantar metatarsal vein and anastomoses with the 

 anterior tibial and saphenous veins. It arises on the outer face of the hock, 

 ascends at first in front of the tendo Achillis, then crosses the latter externally, 

 passes up between the biceps femoris and semitendinosus, and joins the posterior 

 femoral vein. 



There are three chief metatarsal veins. The great dorsal metatarsal vein 

 arises at the distal part of the metatarsus by the union of the dorsal digital vein 

 and a large branch from the venous arch above the sesamoids. It ascends super- 

 ficially between the long and lateral extensor tendons and becomes the chief radicle 

 of the anterior tibial vein. The internal plantar metatarsal vein arises from the 

 venous arch above the fetlock, ascends along the imier border of the suspensory 

 ligament, passes through the vascular canal of the metatarsus and centro-tarsal (as 

 the perforating tarsal) and joins the anterior tibial vein. The external plantar 



