598 ANATOMY AND PHYSIOLOGY OF THE HORSE’S FOOT. 
each other in every possible manner, and compose those mar- 
vellous groups of festoon, tracery, and trellis work which we 
never find ourselves tired of admiring. 
This ingenious combination of elasticity, strength, rami- 
fication, and intercommunication of the arteries is impera- 
tively necessary in order to overcome what would be other- 
wise insurmountable difficulties in this region of the body. 
One of these difficulties is created by the continually 
dependent condition of the limbs, and the tendency of the 
blood to gravitate and pass along too rapidly for the purposes 
of nutrition, especially as there are no muscles to check or 
modify this force of descent ; and another rises from the dis- 
tance between the foot and the propelling organ — the heart. 
The impulse the latter communicates to the vital fluid is 
greatly weakened or dispersed by the obstacles opposed to its 
course in the smaller divisions of the vessels. The elasticity 
and thickness of the tubes, and which latter is providentially 
greatest at their convexities, where the force of the current 
is most felt, compensate in a large measure for the insuffi- 
ciency of the vis a tergo, as the heart's force has been termed : 
augmenting the pulsation and giving a renewed propulsion to 
the blood on its downward course. 
The divisions, subdivisions, networks, circles, and arcades 
of vessels, all more or less related and dependent on each 
other, have also a great influence on the movement of the 
blood in the foot. The exceedingly varied arrangement and 
tortuosity of the multitudinous canals which diverge in every 
direction, facilitate a free current throughout the organ, 
while affording an equable and prolonged supply, by forming 
a kind of reservoir in which an almost unlimited allowance 
of nutrient material can be stored. 
This will be understood better if we imagine two descend- 
ing columns of blood impelled with the same degree of force, 
coming in contact in the interior of a transverse canal, or in 
a cul-de-sac , such as the arcade formed by the reciprocal union 
of two trunks. The immediate result of this afflux of liquid 
must be a considerable distension of the walls of the vessel, 
which is momentarily increased in calibre ; but this widening 
again is opposed, and finally overcome, by the reaction that 
takes place in the thick elastic walls during the intermittence 
in the “systoles" or impulsive efforts of the heart. This 
reaction, it will readily be conceived, gives a fresh impetus 
to the onward current, which was becoming retarded ; and, 
further, this is augmented by the escape of the fluid through 
either the ends of the transverse canal or the ramifications 
springing from the convexities of the communicating circles, 
