126 PHYSIOLOGY OP FARM ANIMALS [CH. 



(7) The body passes over the near fore leg, and is then Hfted 

 off the ground as in the first stage. 



The fore leg in propulsion rotates over the foot, the limb being 

 extended in a straight line from the elbow to the ground. In 

 the case of the hind leg propulsion is obtained partly by the foot 

 being placed on the ground against which it presses, and partly 

 by the straightening of the hock. It is estimated that the hock 

 performs twice the work done by the knee, and this, as will be 

 seen again later, is one of the reasons why the hock is more 

 liable to injury than the knee. 



The Horse's Foot. 



The wall of the "foot' or hoof is composed essentially and 

 developmentally of two layers, (1) the horny part representing 

 modified epidermis, and (2) the internal vascular part repre- 

 senting the dermis. 



The front part of the foot is called the toe ; the hind part the 

 heel ; between are the two quarters. 



The wall is the part of the hoof which is visible when the foot 

 is resting on the ground. The sole is the part which is in contact 

 with the ground. The foot-pad or 'frog' is the pyramidal- 

 shaped part of the hoof filling the space left by the inflection of 

 the walls in the hind part of the hoof. The bars are the inflected 

 portion of the wall running forwards under the foot so as to 

 form an acute angle, within which the frog lies. 



The fore and hind feet are in a general way similar, but the 

 hind feet are narrower and rather more upright. 



The periople is the epithelial varnish covering the external 

 surface of the wall, and thickest at the top of the wall where it 

 forms the perioplic ring. 



Inside the wall, which consists of horny laminae, are the 

 sensitive laminae. 



The coronary cushion is a prominent ring arranged round 

 the edge of the hoof. It is lodged in a special groove in the 

 horn, termed the cutigeral groove. The coronary cushion is 

 continuous with the keratogenous membrane, a highly vascular 

 structure (like the cushion). This membrane is directly inside 

 the sensitive laminae, which themselves dovetail into the in- 

 sensitive lammae of the hoof without. 



