40 . THE ANATOMY OF THE HORSE. 



or true skin. The faminae, it will be noticed, become progressively 

 shorter as they are traced backwards ; and at the end of the series on 

 each side, and adjacent to the plantar cushion, there is a number of 

 small leaves that were interleaved with the horny laminae of the bars. 



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

 placed above the laminae and below the limits of the skin of the digit. 

 It fits into the cutigeral or coronary groove at the upper border of the 

 wall, and its surface is closely set with long papilla) which were received 

 into the apertures found in that groove. These papillae give the 

 coronary cushion a velvety pile, which may be rendered very evident 

 by immersing 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 perioplic ring. 

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

 the cushion and the sensitive laminae. The coronary cushion is a 

 modified portion of the corium, and through the agency of the cells 

 which cover the surface of its papillae the wall of the hoof is formed. 



The Perioplic Ring. This ring is composed of papillae 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 wall is formed. 



The Plantar Cushion. This is a fibro-elastic pad interposed 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 

 surface, and it is moulded on the upper face of the horny frog, to which 

 it has a close resemblance in form. The central portion of the cushion 

 is therefore sometimes termed the sensitive frog, and it is also known as 

 •the pyramidal body. It shows in front a single ridge, which posteriorly 

 becomes divided into two by a deep median cleft for the reception of 

 the frog-stay. This -surface has a villous aspect, the papillae being 

 imbedded in the foramina seen on the upper surface of the horny frog. 

 The horny frog is formed by the agency of the cells covering these 

 papillae. Beneath the surface are some tubular glands, of which the 

 ducts are continued through the horny frog. The upper face looks 

 forwards as well as upwards, and is applied to the reinforcing sheath of 

 the deep flexor tendon. The borders, which are right and left, bring 

 the plantar cushion into relation with the inner surface of the lateral 

 cartilages: The apex lies in front of the semilunar crest of the os pedis, 

 with whose periosteum the tissue of the cushion is intimately blended. 

 The base of the cushion consists of two thick rounded masses termed 

 the bulbs of the plantar cushion. These are continuous in front with 

 the ridges of the pyramidal body, and they present the same velvety 

 aspect; while, on each side, the villous tissue joins the. extremities of 

 the coronary cushion. 



