562 Veterinary-Captain Frederick Smith [May 3. 



small but exceedingly important bone, the seat of an incurable 

 lameness. The question arises as to the use of the navicular bone ? 

 My reply to a rather complex question must be brief — it is to increase 

 the area of the pedal joint. It is obvious that an increase in the 

 area of the joint could have been obtained by making the pedal bone 

 itself larger, instead of introducing a third bone into the joint for 

 the purpose. You will, however, observe from this model that the 

 navicular bone has a movement quite independent of that of the 

 pedis, it gives slightly when I press upon it and then returns to its 

 place. Bearing in mind what I told you early in this lecture that the 

 heel of the foot comes to the ground first in all fast paces, you will be 

 able to see that this small and troublesome bone really forms a 

 yielding articulation, on to which the first force of impact is imparted, 

 and in this way concussion is prevented. When this bone becomes 

 diseased the animal, as we might imagine, goes on its toes and loses 

 all freedom in its gait. 



The next mechanism to be described is the descent of the vascular 

 within the homy foot, a process which can be perfectly seen in this 

 model. The whole of the vascular foot under the influence of the 

 body weight sinks or becomes depressed within the hoof, to rise 

 again to its position when the weight is taken off the limb : to 

 revert to our original simile, the finger slides up and down within the 

 glove. The amount of this movement is about y 1 ^ of an inch. The 

 effect of it is that the foot offers an elastic and not a rigid resistance to the 

 concussion of impact, and in this way neutralises the jar which would 

 otherwise be felt, in the same way that it is easier to catch a cricket- 

 ball by a retreating movement of the hand than by rigid opposition. 



At the moment of the descent of the internal foot, the horny sole, 

 which you will remember is concave towards the ground surface, 

 becomes slightly flattened, as the result of which no bruising of the 

 delicate structures covering the sensitive foot is incurred. 



If we place a foot rule in such a position that one arm is resting 

 on the ground, while the other is lying parallel to the wall of the 

 foot at the toe, and in this position lift up the opposite foot so as to 

 throw double weight on the one under investigation, it will be found 

 that at the moment the extra weight comes on the limb the upper or 

 coronary edge of the hoof slightly recedes from the foot rule ; when 

 the extra weight is taken off the foot, the edge advances into its 

 original place. This phenomenon is associated with a sinking of the 

 upper edge of the hoof at the heels, and an increase in the width of 

 the foot. 



The change in shape just described follows as the result of a 

 temporary rearrangement in position of the parts within. 



We have previously drawn attention to the very vascular nature 

 of the horse's foot ; time will not admit of stoj)ping to enquire into 

 the causes of this vascular condition, but what chiefly strikes the 

 physiologist is that a part lying furthest from the heart should be 

 able to have such a complex circulation carried on with comparative 



