THE BRACHIAL OB AXILLABT ARTERIEi:. 571 



anterior radial artery ; the posterior traverses the inferior radio-ulnar aruh, to distribute 

 the majority of its branches behind the carpal articulations. 



10. Radio-palmar artery. — Arising, as we have already seen, from the po.sterior 

 radial artery, towards tlie upper third of the fore-arm, this branch descends to the 

 superior extremity of the metacarpus in following, as in the Horse, a superficial course 

 and ends in four metacarpal interosseous arteries three posterior or palmar, and one 

 anterior or dorsal. The posterior interosseous arteiies are very irregular and inconstant 

 in their disposition ; they communicate with each other by several branches, and 

 anastomose, inferiorly, either with the lateral digital arteries, the collateral of the cannon 

 or, as is most commonly the case, with a branch of the latter vessel. 'I'hese interosseous 

 arteries are distinguished inte external, middle, and internal ; the first two are comprised 

 between the posterior face of the metacarpus and the suspeuboiy ligament; the third, 

 placed at the inner border of that ligament, is more considerable than the others, and by 

 its volume and direction represents the continuation of the radio-palmar artery. The 

 anterior interosseous artery passes through the foramen at the superior extremity of the 

 metacarpus, and arriving at the dorsal face of the bone, it bifurcates, its ascending 

 branch reaching the capsular ligament of the carpal articulations, where it anastomoses 

 with the divisions of the anterior radial and interosseous arteries of the fore-arm; the 

 descending is lodged in the anterior groove of the metacarpal bone, and joins a perforating 

 branch of the collateral artery of the cannon — a branch which crosses the foramen 

 pierced towards the inferior extremity of the bony diaphysis. If it is desired to ascertain 

 the signification of these interosseous arteries in their relation to the elements composing 

 the foot of Ruminants, we readily recognise : in the posterior median artery, the 

 interosseous palmar of the two great digits; in the posleiior lateral arleries, the 

 interosseous palmar, intermediates to these middle digits, and the rudimeniary lateral 

 digits represented by the ergots or dew claws ; and in the single anterior artery, the dorsal 

 interosseous of the two great digits. W e may even prove, by a more minute examination, 

 the existence of dorsal interosseous arteries corresponding to the latei al palmar inter- 

 osseous vessels. 



11. Collateral artery of the cannon. — This artery follows the same trai-k as in the 

 Horse, as far astlie lower third or fourth of 1he metacarpus. Arrived at this point, it 

 abandons, as in the Horse, a branch whose divisions communicate with the interosseous 

 arteries, and are continued by the digital arteries, three in number: a middle and two 

 lateral (Fig. 319). 



«. The communicating branch with the metacarpal interosseous arteries very often 

 arises from tlie internal digital artery. 



It is insinuated between tlie divisions of the suspensory ligament, and ascends on the 

 posterior face of the metacarpus, breaking up into a number of branches which nearly 

 all join the precited arteries, or even the lateral digital, in affecting a variable and 

 complicated disposition which it is needless to notice here. One of these branches— a 

 true perforating artery, traverses the inferior extremity of the cannon bone, and ascends 

 in its anterior groove to join the anterior interosseous artery, after detaching ramutcules 

 to the metacarpo-phalangeal articulation. 



6. The middle digital artery represents, by its dimensions, the continuation of the 

 collateral artery of the cannon, and is a very voluminous vessel. It is at first inflected 

 backwards and outwards to be placed on the posterior face of the perforatus tendon ; then 

 it descends into the interdigital space by passing behind the great setamoid sheatli, 

 beneath the ligament uniting the two claws. Reaching the inferior extremity of the 

 first phalanx, it divides into two ungueal arteries, one for each digit, which are inflected 

 forwards, pass beneath the internal ligament common to the two intcrphalangeal articu- 

 lations, and enter by the foramen pierced at the inner side of tlie pyramidal eminence 

 Into the internal sinus of the third phalanx, where each ramifles in the same manner 

 as the plantar ungueal arteries of the Horse. 



Several collateral branches, remarkable for the richness of their arborisations, escape 

 from this median artery of the digits and its terminal divisions. The most important of 

 these are : 1, At the middle of the first phalanx, two short transverse branches— a right 

 and left, passing beneath the flexor tendons and going from the median digital artery 

 to the lateral arteries of the digits ; 2, Nearly at the same point, a single artery which 

 traverses the interdigital space from behind to before, to pass between the two tendons 

 of the common extensor of the phalanges, whence it ramifles on the anterior fa,ne of 

 the digits by ascending along the anterior median vein, and anastomosino; with a 

 descending branch of the perforating artery which crosses the inferior extremity of the 

 metacarpus ; 3, A double branch analogous to the artery of the plantar cushion of the 

 Horse, having its origin at the terminal extremity of the digital artery, often arising from 

 the ungueal artery, either on one side or both, and communicating, by a transverse branch, 



