THE VEINS 621 



arteries in forming the proximal plantar arch. Near the distal end of the metatarsal 

 bone it gives off the distal perforating metatarsal artery which passes back through 

 the distal metatarsal foramen and assists in forming the distal plantar arch. The 

 two arches are connected by the small deep plantar metatarsal artery which lies 

 in the groove on the posterior face of the large metatarsal bone. 



The dorsal common digital artery is the direct continuation of the dorsal 

 metatarsal. It divides into two branches which unite in the interdigital space with 

 the corresponding branches of the plantar common digital to form the proper 

 digital arteries. 



The plantar common digital artery descends from the distal plantar arch, 

 anastomoses in the interdigital S])ace with the internal and external digitals, and 

 divides into two branches which join those of the dorsal common digital arterj- as 

 before mentioned. 



The foregoing is a l)rief statement of the more common arrangement of the 

 vessels in the distal part of the limb, but minor variations are very common. 



The Veins ' 



The vena hemiazygos usually takes the ])lace of the vena azygos. It lies 

 along the left side of the aorta and the l)odies of the thoracic vertebrae, turns down 

 across the left face of the aorta and left i)ulmonary artery, runs back over the left 

 auricle and opens into the great coronary vein or the right atrium. It receives 

 the intercostal veins. 



Two jugular veins occur on either side. The internal jugular vein (V. jugu- 

 laris interna) is a relatively small vessel Avhich accom])ani('S tlu- carotid artery. It 

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

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

 .sometimes absent, but in some cases it apj^ears, 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 verj' large and corresponds to the 

 single jugular of the horse. It is separated from the carotid arterj- in the greater 

 part of its course by the sternocephalicus and omo-hyoideus muscles. 



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

 is continued by the internal jugular vein. 



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 

 superior 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 liy transverse branches. They unite near the fetlock 

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

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

 accessory cephalic or the cephalic vein. 



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



^ Most of the differences in the veins of the ox are correlated with those of the arteries of 

 which they are satellites and will not be described. The account here given consists chief!}' of 

 those differential features which could not be deduced from a knowledge of the arteries. 



