THE INTEGUMENTARY APPENDAGES. 



803 



Fig. 373. 



can perceive that it is essentially constituted by adipose tissue.) Numerous 

 blood-vessels and nerves complete this structure. 



B. THE KERATOGENOUS MEMBRANE, OR SUBCORNEUS INTEGUMENT. The 

 keratogenous membrane envelops the extremity of the digit, by spreading 

 over the terminal expansion of the tendon of the extensor pedis, through the 

 medium of a fibrous fascia a dependency of the lateral cartilages ; and also 

 over the inferior moiety of the external face of these cartilages, the bulbs of 

 the plantar cushion, pyramidal body, anterior part of the plantar face of the 

 third phalanx, and over the anterior surface of the same bone. It covers all 

 these parts like a sock, and the hoof incloses it, as a shoe does the human foot. 



This membrane becomes continuous with the skin of the digital region 

 at a circular line that intersects the middle portion of the second phalanx, 

 and inclines obliquely downward from behind to before. Below this line, 

 in front and laterally, the subungular tissues form a semicylindrical pro- 

 tuberance, covered with villi, and designated the " bourrelet." (This 

 elastic prominence has received several most inappropriate names from 

 English farriers and hippotomists, such as " coronary ligament," " coronary 

 substance," " cutiduris," etc. From its function, structure, situation, and its 

 analogy to the plantar cushion, I have designated it the " coronary cushion.") 



On the plantar cushion and the lower face of the pedal bone, this mem- 

 brane is also a villous tunic the velvety tissue, which is continuous, towards 

 the bulbs, with the extremities of the coronary cushion. 



The portion spread over the anterior face 

 of the third phalanx constitutes the laminal 

 or "leafy tissue," so called because of the 

 laminae or parallel leaves seen on its sur- 

 face. 



The three regions of the keratogenous 

 apparatus will be successively studied. 



1. CORONARY CUSHION. This part is the 

 matrix of the wall of the hoof, and is lodged 

 in a cavity excavated at the upper border of 

 this part of the horny case. It forms, ac- 

 cording to the expression employed by 

 M. Bouley, a rounded prominence, which 

 projects like a cornice above the podo- 

 phyllous tissue. 



Its inferior border is separated by a white 

 zone from the upper extremity of the laminsB, 

 which constitute this boundary. 



The superior border is limited by a 

 slightly projecting margin named the peri- 

 oplic ring, because it originates the horn of 

 the periople. Between this margin and the 

 cushion is a sharply defined groove. 



The extremities, narrower than the middle 

 portion, on arriving at the bulbs of the 

 plantar cushion, bend downwards into the 

 lateral lacunae of the pyramidal body, where 

 they become confounded with the velvety 

 tissue. 



The surface of the organ shows filiform prolongations, a little constricted 

 at their base, and named papillae, villo-papillce, villi, and villous loops, whose 



LATERAL VIEW OF THE HORSE'S FOOT, 

 AFTER REMOVAL OF THE HOOF. 



1, Perioplic ring, divided by a narrow 

 groove from the coronary cushion, 

 2, which is continuous with the 

 plantar cushion, 4, and joins the 

 vascular laminae, 3, through the 

 medium of the white zone. 



