720 THE BLOOD-VASCULAR SYSTEM OF THE OX 



arises by occipital, laryngeal, and thyroid radicles, receives tracheal, cesophageal, 

 and muscular branches, and joins the external jugular near its termination. It is 

 sometimes absent, but in some cases it appears, on the other hand, to be large 

 enough to Interfere with venesection practised on the external jugular. The 

 external jugular vein (V. jugularis externa) is very large and corresponds to the 

 jugular of the horse. It is separated from the carotid artery in the greater part 

 of its course by the sterno-cephalicus and omo-hyoideus muscles. 



The ventral cerebral vein usually does not unite with the occipital; the latter 

 is continued by the internal jugular vein. 



The ventral longitudinal sinus is represented by a vein. There is an anterior intercavernous 

 sinus. The transverse sinus is connected with the basilar plexus by a vein which traverses the 

 condyloid canal. In the sheep there are two ventral occipital smuses in place of the basilar plexus. 



The orbital veins form a network between the periorbita and the muscles of 

 the eyeball. This plexus communicates with the cavernous sinus and with the 

 dorsal cerebral vein. It is also drained by the frontal vein, which runs in the 

 supraorbital canal and groove and joins the angular vein of the eye. 



The dorsal nasal vein is usually double. 



The superior labial vein usually joins the infraorbital. 



The vena reflexa is absent, and the radicles which are received by it in the horse 

 go to the internal maxillary vein. 



The sublingual vein is very large. 



The veins of the thoracic limb differ chiefly in the distal part; the special 

 features are as follows: 



The dorsal digital veins ascend on the front of the digits and are connected 

 with the other digital veins by transverse branches. They unite near the fetlock 

 to form the dorsal metacarpal vein. This runs upward on the dorsal face of the 

 metacarpus and carpus, inclines to the medial surface of the radius, and joins the 

 cephalic or the accessory cephalic vein. 



The volar digital veins are larger than the dorsal veins. They lie on the inter- 

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

 is a satellite of the volar common digital artery. This trunk, the volar common 

 digital vein, which is often double, is connected distally by transverse branches 

 with the lateral and medial digital veins to form the superficial volar arch; it is 

 continued upward as the satellite of the ulnar artery. 



The medial and lateral digital veins lie in front of the corresponding arteries. 

 They are cormected 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 medial vein is continued as the medial volar 

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

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

 volar face of the metacarpal bone by the lateral volar metacarpal vein. The latter 

 unites at the proximal part of the metacarpus with the middle volar metacarpal 

 vein, and the trunk thus formed joins the medial vein to form the deep plantar arch. 

 They unite below the carpus or join the volar common digital vein. 



The digital veins arise from the venous plexuses of the corium of the hoof. They form by 

 anastomotic branches a venous circle at the coronary border of the hoof, which may be termed the 

 coronary circle. A vein which emerges from the foramen on the proximal part of the interdigital 

 surface of the third phalanx is the principal radicle of the dorsal 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 border of the 

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



