THE APPENDAGES OF THE SKIN. 



915 



Prolonged maceration separates it into three portions — the tvall, sole, and 

 frog. 



Wall. — The wall — also named the crust — is that part of the hoof which is 

 apparent when the foot rests on the ground. This thick plate of horn covers 

 the anterior face of the foot, and, gradually narrowing in width and diminishing 

 in thickness, passes round each side until it reaches the bulbs of the plantar 

 cushion, when its extremities are sharply inflected inwards, between the frog and 

 internal border of the sole, becoming confounded with the latter about its middle 

 or anterior third, after being greatly reduced in breadth and substance. 



The middle— or anterior part — of this horny envelope is popularly known as 

 the toe ; its two sides are designated outside and inside toe ,- the lateral regions con- 

 stitute the quarters ; the heels are formed by the angles of inflection of its 

 extremities ; while these extremities themselves, passing along the inner border 

 of the sole, are termed the bars. 



Examined with regard to the direction it follows in its relations with the 

 ground, this envelope is seen to be much inclined in its middle region or toe, and 

 this obhquity gradually diminishes until the 

 posterior part of the quarters is reached ; at 

 this point the wall is nearly perpendicular. 



The following are the characters it offers 

 in the conformation of its faces, borders, and 

 extremities : — 



The external face, convex from side to side, 

 and perfectly straight from the upper to the 

 lower border, is smooth, polished, and shining : 

 an appearance it owes to a thin horny layer, 

 independent of the wall proper, designated the 

 periople. 



This periople forms, on the upper part of the 

 wall, a kind of ring, continuous with the bulbs 

 of the plantar cushion, and with the frog, of 

 which it is only a dependency ; responding, by 

 its upper margin, to the perioplic ring, which 

 secretes it ; towards the lower part of the wall 

 it is gradually lost, friction incessantly thinning 

 and destroying it. 



The inner face presents, over its entire ex- 

 tent, the white parallel leaves which dovetail with the laminae of the podophyllous 

 tissue. Collectively, these are named the Iter aphyllous tissue. 



The superior border is bevelled off, on its inner aspect, into a circular con- 

 cavity, into which the plantar cushion is received. This excavation is named 

 the cutigercd cavity, because of its relations ; it offers on its surface a multitude 

 of minute openings — the commencement of the horny canaliculi which receive 

 the villosities of the cutiduris. 



The inferior border, in contact with the ground, and subjected to wear in 

 unshod animals, is united inwardly, and in the most intimate manner, with the 

 circumference of the sole. 



The extremities, constituted by the reflected and re-entering prolongations 

 known as the bars,iorm, outwardly, the external side of the lateral lacunge of the 

 frog ; they are provided, inwardly, with laminas like the rest of the wall. The 



HOOF JUST REMOVED FROM THE 

 FOOT (SIDE view;. 



Inner surface of periople, or coronary 

 frog-band, with some hairs passing 

 through ; a', outer surface of same 

 at posterior part of foot ; a", a 

 section through the wall to show 

 its thickness; 6 to c, quarter of the 

 hoof, from b to the front is the out- 

 side (or inside) toe ; from c to d the 

 outside (or inside heel) ; e, frog ; /, 

 bevel on upper margin of wall for 

 reception of coronary cushion ; g, 

 keraphylla, or horny laminae. 



