THE FORE EXTREMITY. 215 



enter the bone througli the foramina on its plantar 

 surface. Branches running downwards through the sub- 

 stance of the bone from this circulus arteriosus of the 

 foot pass out of the large foramina at the outer margin of 

 the plantar surface of os pedis, where they form a continu- 

 ous arterial circle, the circumflex artery of the toe, which 

 receives branches superiorly from the lateral laminal arte- 

 ries, which sometimes mainly form it ; and on the plantar 

 surface some large arteries (solar) radiate to it from the 

 artery of the apex of the frog. It will be thus seen that 

 the arteries form an intricate plexus, not only in the sensi- 

 tive structures, but also in the bones of the foot ; the veins 

 are more numerous, they form an intraosseous plexus, the 

 vessels of which mainly converge to a trunk corresponding 

 to the plantar arteiy inside the lateral cartilage ; and also a 

 superficial plexus composed of vessels with but small meshes, 

 which are found in the whole of the vascular investing and 

 secreting layer of the foot, they converge towards certain 

 larger veins which are on the external surface of the lateral 

 cartilages and form a vein which unites above the cartilage 

 with the intraosseous vein to form the plantar which runs 

 upwards (receiving branches), with and in front of the artery 

 to unite with its fellow above the fetlock. From this junction 

 four or five vessels inin upwards, bemg the satellites of the 

 large and small metacarpal arteries, and form the radial and 

 superficial brachial veins respectively; since the smaller veins 

 of the foot have no valves, they can be injected from the 

 plantar. 



After passing with the flexor tendons through the annu- 

 lar ligament of the knee, the metacarpal nei*ves accompany 

 the tendons as far as opposite the superior part of the 

 inferior third of the large metacarpal bone. The external 

 metacarpal nerve is derived from the ulnar, the internal 

 metacarpal nerve from the radial. The internal gives olf 

 fibres which form a trunk extending obliquely downwards 

 and outwards between the skin and the flexor tendons to 

 the external metacarpal nerve. At the side of the fetlock 

 each nerve divides into three parts ; one runs over the front 

 of OS suffraginis ; it is separated by the plantar vein from 

 the middle branch which runs to the coronet, and is 

 separated by the plantar artery from the posterior plantar 

 nerve which supplies the major portion of the foot witfe 

 nerve force. 



