104 ANATOMICAL STEUGTUEE OF THE SHEEP. 



is rudimentary. Tlie principal metacarpal bone is furrowed 

 tlirougliout its entire length by a deep fissure, a trace of primi- 

 tive separation of the bone in two pieces, the posterior face 

 being also similarly marked. Below the metacarpus we find 

 four bones or digits, two of which are perfect. Behind the 

 articulation of the metacarpus and digits are two small bones 

 called sesamoids, which serve as levers, over which tendons pass. 

 The bone of the foot or os pedis is also double, and articulating, 

 superiorly with pasterns, gives the conformity of cloven foot. 

 The foot is formed by the coffin bones and navicular, two of 

 each, surrounded by a horny box, as an outside protection to the 

 sensitive parts overlying these bones. 



The lower and back part of the coffin bone is attached to an 

 elastic pad of a fibrous nature, which by its elasticity minimizes 

 the conciission consequent to the weight of the animal being 

 suddenly thrown on the foot. This pad, resting on the horny 

 heels, supports the principal part of the animal's weight, very 

 little being communicated to the toe of the foot. In sheep the 

 crust of the foot is secreted by a vascular structure, the coronary 

 substance which in the horse secretes the greater part of the 

 crust, being absent in the sheep. The sole of the foot is 

 secreted from the vascular membrane situated immediately 

 above it, called the sensitive sole, there being a considerable 

 thickness of this dense substance between the coffin bone and 

 horny sole. This explains why, in sheep with foot rot, the foot 

 can be so quickly restored, as when the horn is lost it is imme- 

 diately replaced from the structure under it, and there is not the 

 delay as in the horse, where the secretion is mainly formed from 

 the coronary substance. 



The inside of the crust, between the toes or cleft of the foot, 

 is much thinner than that portion on the outer side, and it is here 

 that foot rot most frequently commences. The horny part of 

 the foot consists of the crust, or outer shell, and sole. The crust 



