ANATOMY AND PHYSIOLOGY OF THE HORSE^S FOOT. 601 
multiplication of the arterial system in the intercostal and 
other vertebral branches, which forms an extensive reservoir 
of blood for the brain. In other instances, we have the 
great tortuosity of vessels alone present, as in the carotid 
artery of the seal, which is nearly forty times longer than the 
space it traverses. 
In the arrangement of the veins we find, perhaps, even 
more ingenuity displayed than in that of the arteries, in order 
to permit the return of the blood towards the heart as freely 
as possible. We have already observed, when speaking of 
the venous system, that the vessels which immediately spring 
from the terminations of the capillary or arterial ramifications 
compose a network so even, though so modified and compli- 
cated, that it is impossible to distinguish the course of any par- 
ticular branch ; also that this arrangement is double : an ex- 
tensive superficial network external to the bone of the foot and 
covering its surface, and an internal less considerable, accom- 
panying the branches of the plantar artery within the bone. 
The sum total of these two reticulations offers a greater capa- 
city than that of the arteries, the blood passing from the latter 
entering larger canals ; and though this might appear to favour 
a slower movement of that fluid, yet it is rendered necessary 
in order to facilitate a free circulation. This disproportion 
between the two systems is more or less manifest in other 
parts of the body ; but the necessity for it is most apparent 
in independent organs, like the limbs, where the circulation 
has to overcome the effects of gravitation. 
As has been indicated by a celebrated French veterinary 
anatomist, the superficial disposition of the most considerable 
part of the venous network of the foot is a condition very 
favorable to the circulation in the whole of the canals ; for 
it puts it immediately under the influence of the general and 
uniform pressure that the enveloping horny box exercises at 
each movement over the whole extent of the membranes 
with which it is in intimate contact and union. Every time 
the foot is placed on the ground, the third phalanx, on which 
is concentrated the final resultant of all the movements of the 
heavy mass of the body, is pushed, as it were, deeper into the 
hoof containing it, and its surrounding membranes, included 
as they are between its external face and the inner aspect of 
the hoof, are submitted to a degree of pressure which drives 
out of them much of, if not all the blood they contain. This 
fact can be readily and strikingly demonstrated by opening 
the circumflex or any of the solar veins, an operation yet 
performed by some veterinarians for the cure of disease. 
The blood flows slowly from the wound unless pressure be 
