712 THE VEINS. 



The two deep anterior veins are email vessels which accompany the collateral artery of the 

 cannon, which is placed between them. They arise in the iuterdigital space from the anterior 

 digital vein, coininunicating, by the inferior metatarsal foramen, with the sesamoid arch, 

 sending off on their way transverse anastomoses, and being continued above the tarsus by the 

 two anterior tibial veins, whose roots they constitute 



The anterior superficial vein is very voluminous. It proceeds from the sesamoid arch, 

 receives near its origin the middle digital vein, rises in front of, and a little to the outside of, 

 the tarsus, communiciiting at this point witli the anterior tibial veins; it divides ahnve the 

 tibio-tarsal articulation into two branches: a posterior, forming the anterior root of the external 

 saphena ; the other anterior, joining the anterior tibial vein of the exterual side. 



The two posterior veins spring from the sesamoid arch. Situated at first between the sus- 

 pensory ligament of tiie fetlock and the posterior face of the metatarsus, and communicating 

 there by several anastomoses, these two veins are continued along the tarsus— the one within, 

 the other without. The internal follows the corresponding plantar artery, and is prolonged in 

 the tibial region by the posterior tibial and internal saphena veins. The external ascends 

 within the calcis, and is united to a branch of the anterior superficial metatarsal, to form the 

 external saphena vein. Before leaving the deep situation they occupy below tiie suspensory 

 ligament of the fetlock, these two vessels — but especially the internal — concur to form a perfo- 

 rating branch which traverses the cuboido-scaphoid canal to join the anterior tibial veins. 



G. Veins of the Anterior Foot in the Ox. — Four digital wiws escape from the two 

 subungual plexuses : an anterior, posterior, and two lateral. 



a. The anterior digital vein, which is very slender, is lodged superficially between the 

 two digits, and comports itself at its origin like the analogous vein of the posterior limb, in 

 rising by two roots. In being prolonged above the fetlock, it constitutes a subcutaneous meta- 

 carpal branch, which occupies the anterior and internal plane of the cannon, and is united 

 above the knee to the principal cutaneous vein of the forearm. 



6. The posterior digital vein— ofiew doubled by a small accessory branch — accompanies the 

 common digital artery, and extends along the collateral artery of the cannon, to constitute one 

 of the posterior radial veins. 



c. The internal digital vein, after passing the digital region, is lodged between the cannon 

 bone and the internal border of the suspensory ligament, proceeds outside the carpal sheath 

 with the radio-palmar artery, and divides above the knee into two branches — an anterior, the 

 origin of the internal subcutaneous vein of the forearm ; the other posterior, forming one of 

 the posterior radial veins. 



d. The external digital vein occupies, on the outer side of the external digit and the cannon 

 bone, a position analogous to the internal vein. It gives rise to several deep metacarpal veins 

 which anastomose, and are mixed with the interosseous palmar arteries ; the principal vein and 

 its accessory branches are joined, below the carpus, to the internal vein. 



It is to be remarked that these four digital veins communicate, in the interdigital space, 

 by anastomoses resembling those of the posterior limb; and that the last three, or principal 

 veins, anastomose above the fetlock in forming a complii'ated and variably arranged sesamoid 

 arch, on leaving which these digital veins become metacarpal vessels. 



Comparison op the Veins in Man with those of Animals. 



In Man, as in animals, the veins are grouped into those of the lesser circulation — or pid- 

 monary veins — and those of the greater circulation. The latter open into the heart by three 

 trunks — the cardiac veins, and superior and inferior vena cava. 



The superior vena cava represents the anterior vena cava of animals, and receives the blood 

 from the veins of the head, thoracic limbs, and a portion of the chest. It extends from the 

 first costal cartilage to t!ie heart, and commences after the junction of the two brachio- 

 cephalic trunks or innominate veins. 



The superficial veins of the thoracic limb at first form, on the back of the hand, a plexus 

 of elongated meshes from which the median, radial, and ulnar veins spring. Near the bend of 

 the elbow, the median bifurcates and gives rise to the median cephalic and median basilic. 

 Blood is abstracted from one or other of tliese branches. At the arm, all tiie superficial veins 

 constitute but two trunks — the cephalic and basilic veins. The deep vessels join these to form 

 the axillary vein, whicli becomes the stihclavian below the clavicle, then the brachio-cephalic 

 trunk {vena innominata) when it receives the internal jugular. 



The venous sinuses of the cranial dura mater are proportionately more developed than ia 

 Solipeds, though they have the same arrangement. There is constantly present a middle or 

 inferior longitudinal sinus. 



The jugulars, which carry the blood from the cranium and face to the heart, are four in 



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