GENEEAL OBSEEVATIONS 



67 



This wedge-shaped structure we have already described as 

 occupying the irregular space between the two lateral 

 cartilages, the extremity of the perforans tendon, and the 

 horny frog. 



Now, when weight or pressure is exerted from above on 

 to this organ, and the fro(i is in contact with the ground 

 below, it is clear from the position the cushion occupies 

 that, whatever change of form pressure from above will 

 cause it to take, it must certainly be limited in various 

 directions. 



Fig. 37. 



The dotted lines iu this diagram represent the expansion of the solar edge 

 of the hoof at the moment of over-extension of the fetlock -joint ; b, the 

 dotted line represents the change in form of the coronary edge under 

 similar circumstances. 



Because of the shape of the cushion its change of form 

 cannot be forwards (simultaneous pressure from above and 

 below on to this wedge with its apex forwards must tend to 

 give it a backward change of form). Because of the pastern 

 being horizontal, and aiding in the downward pressure, its 

 change of form cannot be upwards. And because of the 

 ground it cannot be downwards. It follows, therefore, that 

 the movement must be backwards and outwards, being 

 especially directed outwards because of its shape and the 

 median lacuna in its posterior half — this latter, the lacuna. 



