CIRCULATORY SYSTEM. 213 



venous netting. We have seen that the arteries of the foot elude 

 pressure, and consequent impeded or interrupted circulation, by 

 piercing the substance of the os pedis; we now perceive that the 

 veins, running all outside (for, to have admitted them also through 

 it, the bone must have been perforated in so many places that it 

 would have become physically inadequate to the superincumbent 

 burden), guard against the impediments constantly occasioned to 

 the circulation in some one or other of them by the numbers of 

 communicating canals crossing in every direction : in addition to 

 which, in order to give every facility to the flow of blood through 

 them, they are unprovided with valves. 



The veins of the sole pour their blood into the veins of the la- 

 minte, with the exception of some few of the posteriormost, and 

 they end in the veins of the frog. 



The veins of the liuni)t(Z increase in size as they approach the 

 coronet, and gradually unravel themselves so as to form a great 

 many plexuses or bunches, which run directly upward, crowd 

 through the substance of the coronary ligament, and afterwards 

 collect into the superjicial coronary vei)i. From them also, larger 

 branches proceed laterally, to be united in tranverse communi- 

 cation by the deep coronary, a vein commonly double. From 

 this the larger veins upon the sides diminish in number, and all 

 conjoin into two or three branches, which, opposite to the pastern- 

 joint, unite into a single vein. 



The veins of the frog, after ramifying in the form of network 

 over that body, ascend along the inner sides of the cartilages into 

 the heel, converging and uniting into larger vessels as they leave 

 the foot, and finally forming a single vein upon the pastern-joint, 

 which runs up and unites, a little above the head of the os suf- 

 fraginis, with that coming from the laminse, thereby forming the 

 plantar vein. 



The plantar vein ascends in front of the plantar artery, keep- 

 ing company with that vessel until both unite with their fellow 

 venous and arterial trunks of the opposite side, and become 

 metacarpal. In its course, it is joined by the perpendicular 

 vein, besides other small unimportant branches : at its termina- 

 tion, it receives one or two veins of considerable size which 

 emerge from the fetlock-joint. 



The metacarpal veins, two in number, result from the 

 union of the plantar; and this takes place in the form of an 

 arch immediately over the sesamoids, in the interval between the 

 flexor tendons and the suspensory ligament. These veins pursue 

 their course up the leg, one on either side, along the same cor- 

 rcs|)ondent channels, between the tendons and the ligament, to 

 the back of the knee, where thcv end in a remarkable anasto- 



