38 THE ANATOMY OF THE HORSE. 



the hoof, is a stratum of soft protoplasmic epithelial cells by whose 

 growth and multiplication the hoof-horn is fomied. This stratum of 

 cells represents the deepest cells of the rete mucosum in the skin, and 

 it is bv its ready decomposition that the bond of connection between 

 the sensitive and insensitive structures is destroyed, permitting the 

 extremity of the digit to be extracted from its horny investment. 



Directions. — The student should next turn his attention to the ex- 

 tremity of the digit as exposed by the removal of the hoof, and he will 

 find it to present a configuration not unlike the exterior of the hoof itself 

 (Plate 10, figs. 1 and 5). And in the first place, let him examine that 

 part which he will easily recognise as having been separated from the 

 inner siiiface of the wall. This is traversed by a series of leaves which, 

 in contradistinction to those already seen on the inner surface of the 

 wall, are termed the sensitive laminae, and sometimes the podophyllous. 

 tissue. 



The Sensitive LAMixiE. Each lamina is fixed by one of its borders to ' 

 the periosteum of the os pedis, and extends in a vertical direction from 

 near the coronary cushion to the sharp edge of the bone, whei'e it 

 terminates in five or six long papillae. In the natural state the sensitive 

 and the horny lamina) are interleaved, and the former here represent 

 the corium, or true skin. The lamina), it will be noticed, become pro- 

 gressively shorter as they are traced backwards ; and at the 'end of the 

 series on each side, and adjacent to tlie plantar cushion, there is a number 

 of small leaves that were interleaved with the horny lamina) of the bars. 

 The CoROXARY Cushion. This is a projecting, cornice-like structure, 

 placed above the lamina) and below the limits of the skin of the digit. 

 It fits into the cutigeral groove at the upper border of the wall, and its 

 surface is closely set with long papilla) which Avere received into the 

 apertures found in that gi-oove. These papillae give the coronary 

 cushion a velvety pile, which may be rendered very evident by immei-s- 

 ing the foot in water. If the coronary cushion be traced backwards, it 

 will be seen to pass into the plantar cushion. Above the cushion is a 

 narrow groove separating it from the periopolic ring. Below the cushion 

 there is a narrow smooth space which runs between the cushion and the 

 sensitive lamina). The coronary cushion is a modified portion of the 

 corium, and through the agency of the cells which cover the surface of 

 its papilla), the wall of the hoof is formed. 



The Perioplic Ring. This ring is composed of papill.T) like those of 

 the coronary cushion, but smaller in size ; and it is by its agency that 

 the periople which covers the exterior of the Avail is formed. 



The Plantar Cushion. This is a fibro-elastic pad intei'posed between 

 the horny frog and the terminal part of the perforans tendon. It 

 possesses two faces, two borders, a base, and an apex. The lower face 

 looks backwards as well as downwards when the foot rests on a flat 



