7D THB horse's foot, etc. 



formed by the commissures. — They each, at b, support the 

 part marked b in Figs. 21 and 22. 

 e c. Are portions of the same projections, and are situated just under 

 the two ends of the navicular bone, and mark the point on 

 either side where diminution in the natural elasticity of the 

 fatty frog would be felt with the greatest severity by the na- 

 vicular joint : for under the most favorable circumstances, the 

 quantity of cushion between these points and the navicular joint 

 cannot be very large ; and hence the importance of our doing 

 all we can to preserve its elasticity as long as possible. 



Figs. 21 and 22, being sections of the foot, are calculated 

 to impart a false idea of the extent of protection afforded to 

 the navicular joint by the elastic cushion, if they are not 

 considered in conjunction with Fig. 23 ; for the cushion, being 

 cut through at the part occupying the hollow between c c. 

 and dy which is its deepest part, would lead to the conclusion 

 that the same quantity of protection was extended to the whole 

 of the joint, if we did not observe that the projections of the 

 commissures c c, Fig. 23, lie nearly on a level with the top 

 of the frog stay, a, showing that there is not space for an 

 equal quantity of cushion between them and the navicular 

 joint, as there is between the navicular joint and the bottom 

 of the hollow at d ; — and it is evident, that if the cushion at 

 these places be not kept in a sufficiently elastic condition to 

 guard the delicate membranes of this important joint from 

 the consequences of being compressed between the navicular 

 bone and these horny projections, injury to the joint must 

 ensue, and unsoundness of the foot become inevitable. 



Having seen the changes that have occurred to the fatty 

 frog of Fig. 21, we shall naturally be led to inquire if the sen- 

 sitive frog has fared any better ; to which end we must first 

 examine it in Fig. 22, where we shall find it distinctly mark- 

 ed at g, and by tracing it over the frog stay, a, we shall see 

 that it extends over the whole surface of the horny frog, be- 

 tween it and the fatty frog : but we shall in vain look for it in 

 Fig. 21 ; the constantly increasing compression it has received, 

 between the gradually hardening cushion, and the horny frog, 

 has by degrees so effectually caused its absorption, that not a 

 vestige of it remains — as is shown by g^ Fig. 21. 



The diminution that has taken place in the horny frog of 

 Fig. 21 will be made sufficiently evident by a comparison 

 of the parts marked d andy', with the same parts in Fig. 22. 



THE END. 



