104 VETERINARY PHYSIOLOGY 



dense fibrous tissue which on its surface is raised in numerous 

 ridges with side branches the sensitive lamellae, vertical in 

 direction in front and oblique posteriorly, and on the surface 

 of these is formed the great epithelial structure, the horny hoof 

 (H.), comparable to an exaggerated nail. In this the anatomical 

 point of importance is the fact that it is very dense and hard 

 in front and softer and more elastic behind, especially in the 

 region of the prominence on the sole called the frog. 



As the foot is brought down the heel first comes to the 

 ground and, in the natural condition, shock is prevented by 

 the elasticity of the posterior part of the foot, due to : 



1. The elastic horn of the frog ; 



2. The almost transversely disposed lamellae ; 



3. The elastic lateral cartilage and intermediate tissue ; 



4. The pressure being transmitted from the coronal bone 

 through the elastic sling of the navicular bone and perforans 

 tendon. 



The alternate compression and expansion of these structures 

 lias the effect of massaging the blood out of the veins of the 

 foot and of thus assisting its onward propulsion, a matter of no 

 small importance in such dependent structures as the feet. 



As the foot is raised it is the toe which last leaves the ground, 

 driving the body forward and upward, hence the hard resistant 

 character of the hoof in front, its firm and direct connection 

 with the pedal bone, the vertical direction of the lamellae, and 

 the arrangement by which as the corouopedal joint is flexed the 

 pressure is transmitted directly from one bone to the other. 



4. THE CHIEF RECEPTOR MECHANISMS 



THE SENSES 



In order that each particular kind of change in the sur- 

 roundings of the body may produce its appropriate reaction, 

 it is essential that the different kinds of changes should act 

 in different ways that the contact of gross matter, changes 

 of temperature, vibrations of the air, vibrations of the ether, 

 and various chemical changes should produce their special 

 effects. 



To secure this, as we have already seen, special peripheral 



