640 THE ARTERIES. 



b. The plantar ungual artery ought to be regarded as a continuation of the 

 digital artery, because of its volume and direction. Lodged at firet, with a fine 

 nervous branch, in the plantar fissure, it afterwards enters the canal of the same 

 name, and thus penetrates into the semilunar sinus of the os pedis, where it 

 anastomoses by inosculation with the opposite artery, forming a deep vascular 

 arcade which we designate the plantar arcade or circle, or, after M. H. Bouley, 

 the semilunar anastomosis (Fig. 377, 12). 



Two orders of branches emanate from the convexity formed by this anasto- 

 motic loop. The ascending order " irradiate in the spongy framework of the 

 third phalanx, and like so many hair-roots, escape by numerous openings from 

 its anterior face, where they form a very intricate plexus by anastomosing, in the 

 texture of the lamina! tissue, with the extreme divisions of the anterior branch 

 of the digital artery and those of the coronary circle. . . . It is to these divisions 

 that Spooner has given the name of anterior knninal arteries " (H. Bouley). 



The descending order, much more considerable, named by Spooner (W. C, of 

 Southampton) the inferior communicating arteries, arise at a right angle from the 

 anterior circumference of the semilunar anastomosis, traverse in a divergent 

 manner the tissue of the phalanx, and make their exit by the large foramina 

 situated a little above the inferior border of the bone, where they furnish a mul- 

 titude of ascending ramuscules which Concur to form the arterial network of the 

 laminal tissue. " Then they anastomose transversely* by a succession of little 

 arcades which are thrown from one to the other, and in this way give rise to a 

 great circumflex canal which follows the contour of the parabolic curve exhibited 

 by the thin border of the os pedis, on its inferior face" (H. Bouley). This 

 vascular arch, which we pui-pose naming the inferior circumflex artery of the foot 

 (Fig, 377, 12), to distinguish it from the circumflex of the coronary cushion, is 

 joined by its extremities to the preplantar artery, in the same manner that the 

 latter circumflex is united to the artery of the plantar cushion. From its con- 

 cavity it throws off some fourteen or fifteen convergent branches, which are 

 destined to the villous tissue of the sole. 



Differential Characters of the External Iliacs in the other Animals. 

 1. External Iliac Arteries of Ruminants. 



In the Ox, apart from the considerable volume of the great muscular arteries of the thigh, 

 the external iliac, as well as the femoral and popliteal arteries continuing it, comport themselves 

 almost the same as in the Horse. It is only when we reach the posterior and anterior tibial 

 arteries that we find some peculiarities worthy of notice. 



Posterior tibial arterij — Much more voluminous than that of Solipeds, this artery follows 

 the same course, and terminates in an analogous manner : forming at its lower extremity two 

 plantar branches, which anastomose witli the perforating pedal artery behind the superior ex- 

 tremity of the principal metatarsal bone, and beneath the suspensory ligament. But these two 

 branches are lar from possessing the same volume ; the internal is incomparably the largest, 

 and appears to be the direct continuation of tlie posterior tibial artery. 



From this anastomosis results, as in the Horse, two series of metatarsal branches — a deep 

 and a superficial. 



The deip branches, two or three in number, form on the posterior face of the metatarsal 

 bone, below the suspensory liL;ament, the posterior interossese, mixed with two or three reticu- 

 lated venous branches ; they anastomose by their inferior extremity with a perforating branch 

 of the collateral of the cannon. 



The superficial branches, similar to tliose which accompany the plantar nerves in the Horse, 

 are of very unequal calibre ; the external is so rudimentary that it often escapes <lissection ; 

 the internal in reality continues the plantar artery of the same side. Both are united to the 

 perforating branch already noticed. 



