ANATOMY AND PHYSIOLOGY OF THE HORSE'S FOOT. 603 
and inflammation of the laminae. Horsemen who have only had 
observation for their guide, and were unacquainted with the 
physiological reasons for such a measure, have long followed 
the practice of walking a horse about after a journey, in order 
to prevent “ stiffness” ensuing. 
Veins, as is well known, are thinner in their walls than 
arteries, and possess but little elasticity ; therefore, in certain 
situations they are particularly liable to over distension. 
This is the case in the limbs of the horse (and, of course, of 
other quadrupeds whose extremities are maintained in a per- 
pendicular position), where the weight of the column of 
blood, which is sometimes as much as four and a half feet 
high, has to be overcome. The pressure of the column is 
equal to one seventh of the pressure of the atmosphere ; and 
it is to contend with it that the veins of the legs are pro- 
vided with valves, which are directed across the interior of 
the vessels, looking towards the heart or upper part of the limb ; 
when two or more have their free borders in apposition, they 
effectually prevent any fluid from passing downwards. These, 
placed at various distances along the inner face of the vein, 
successfully oppose the reflex or descent of the blood which 
has already been forced onwards. The immortal Harvey's 
general description of them is quite applicable to those in 
the veins of the horse’s limbs. In many places two valves 
are so placed and fitted that, when raised, they come exactly 
together in the middle of the vein, and are there united by 
the contact of their margins ; and so accurate is the adapta- 
tion, that neither by the eye nor by any other means can the 
slightest chink along the line of contact be perceived. But 
if the probe be now introduced from the extreme towards the 
more central parts, the valves, like the flood-gates of a river, 
give way and are most readily pushed aside.”* 
By their means, the long column of blood is divided into 
a large number of secondary columns, each of which rests 
alternately upon an ascending pair of valves; so that the 
comparatively feeble moving power that propels the blood 
through the veins is only required to overcome in succession 
the fractional resistance offered by each segment of the 
column instead of the whole ; therefore it is that their pre- 
sence in the veins of the limb, and their complete functional 
integrity, is an absolutely necessary condition of healthy 
circulation. 
But these valves do not descend below the coronary plexus 
of veins, and are, therefore, not to be found in any of these 
vessels in the foot. There they would be more damaging 
* *■ On the Motion of the Heart and Blood/ Edit. Sydenham Society. 
