THE EXTERNAL ILIAC ARTERIES. 639 



tions : one posterior, placed above the superior border of the small sesamoid, 

 beneath the perforans tendon ; the other anterior, more extensive and volmniaous, 

 covered on the sides by the lateral cartilages of the foot, and in its front or 

 middle part by the expansion of the anterior extensor tendon of the phalanges. 



The collateral ramuscules furnished by the posterior part of the circle are 

 small, few, and of no interest. 



Among the branches arising from the anterior portion, there is only a single 

 pair of arteries to be noted, which are remarkable for their mode of distribution 

 and their volume. They originate near the border of the extensor tendon, and 

 immediately divide into two divergent branches : one the internal, which passes 

 across that tendon to anastomose with the homologous branch of the opposite 

 side ; the other, external, passes backward to meet the cutigeral branch furnished 

 by the artery of the plantar cushion, and joins that vessel. From this disposi- 

 tion results a very fine superficial vascular arch around the coronet, which is well 

 named the circumflex artery of the coronary cushion ; it is situated a little above 

 the cutidural artery, beneath the skin of the coronet, and looks as if encrusted in 

 that membrane ; by its two extremities it rests on the arteries of the plantal 

 cushion, and is fed by the two principal vessels of the coronary circle ; while it 

 furnishes ascending anastomosing ramuscules to the inferior divisions of the per- 

 pendicular artery, as well as numerous descending branches passing into the 

 coronary cushion and the laminal tissue of the foot. 



Such is the ordinary disposition of the coronary circle and its superficial arch 

 — the circumflex artery of the coronary substance ; though it varies much in 

 different animals, and even in the feet of the same animal. To attempt to 

 describe here the variations we have seen would be supererogatory, and we may 

 hmit ourselves to saying that these varieties were almost exclusively confined to 

 the origin of the branches composing these two circular vessels and their manner 

 of arrangement, without modifying in any way the general disposition of the 

 circles.' 



Terminal divisions. — These are, as has been ah-eady mentioned, the plantar 

 and preplantar ungual arteries.^ 



a. The preplantar ungual artery is the smallest of these two terminal branches. 

 Situated at first inside the basilar process of the third phalanx, it turns round 

 this to traverse the notch which separates this process from the retrossal eminence, 

 is lodged with a satellite nerve in the preplantar fissure, which it crosses from 

 before to behind, and terminates near its anterior extremity by several divisions 

 that bury themselves in the os pedis. In its course, it distributes : 1. Before 

 passing into the sub-basilar notch, a deep retrograde branch destined to the bulb 

 of the heel and the villous tissue. 2. Immediately after leaving that notch, a 

 second retrograde branch, whose divisions pass backward, behind the great 

 circumflex artery of the pedal bone. 3. During its passage in the preplantar 

 fissure, several ascending and descending branches which ramify iu the laminal 

 tissue ; the firet anastomose with the descending divisions of the coronary circle 

 and the circumflex artery of the coronary cushion. 



* We may notice here one of these variations, which is somewhat frequently met with in 

 the anterior limb. This consists in the anterior descending branch of the perpendicular artery 

 uniting at its terminal extremity with the circumflex artery of the coronary substance, which 

 it concurs to form. 



* In all treatises on anatomy, these vessels are simply designated the plantar and preplantar 

 arteries. We have added the epithet ungual to distinguish these arteries from the properly 

 so-called plantar bmnclies— the terminal divisions of the posterior tibial artery. 



