GENERAL CONCLUSIONS ON EXPANSION. 



123 



In order to understand the mechanics of the hoof, it is 

 desirable to study the changes in movement somewhat more 

 closely. According to 

 Peters' theory, the pedal 

 bone, with its comple- 

 mentary parts, the na- 

 vicular bone and lateral 

 cartilages, rotates in the 

 segment of a circle 

 around its own point, 

 which is to be regarded 

 as its axis. If we bear 



in mind that the inter- fig. 69.— vertical cross section of a foot seen from behind. 



., 1 1 • '^' coronet bone; B, navicular bone; C, pedal bone; 



Vals between the elastic «, lateral cartilage ; b, anterior portion of plantar 

 ^ . cushion ; c, divided part of flexor pedis perforans ten- 



lamillie and the horny don ; rf, postero-lateral ligaments of navicular bone ; ^, 



, - . horn wall ; ?« , horn sole ; n, white line ; o, horn frog. 



wall mcrease towards 



the heels (Fambach), it will be seen that the connection 

 between the sensitive and horny laminae is not everywhere 

 equally firm, but becomes less so towards the heels, and, there- 

 fore, that at this point the greatest movement might theoreti- 

 cally be looked for. In consequence of its formation, its strong 

 and long wall, and its connection with the pedal bone, the toe 

 would be expected to suffer least displacement under pressure, 

 whilst the posterior parts of the hoof, being less thick and less 

 firmly attached to the bone, would yield to a greater extent. 

 In its descent the os pedis tends to draw the lamime backwards 

 and downwards, so that their inner margins, instead of pointing 

 towards the centre of the foot, tend to point towards the bulbs, 

 a condition which results in slightly diminishing the height of 

 the hoof, diminishing the diameter of the toe and lateral parts 

 of the coronet, pressing backwards the bulbs, causing the 

 posterior parts of the sole to descend and the heels to widen. 

 Immediately pressure is removed, the laminae seek to return to 

 their former position and thus restore the normal state of the 

 foot. 



At the time when the fetlock is most extended, the lateral 

 cartilages and plantar cushion also come more prominently 

 into play. The posterior, i.e., the broadest, part of the coronet 

 bone glides backwards and downwards between the lateral car- 

 tilages, thrusting them apart, and through the medium of the 



