892 THE SENSE ORGANS AND SKIN OF THE HORSE 



is the densest part of the hoof. Its horn tubes run in a straight direction from the 

 coronary to the basal border. In dark hoofs it is pigmented except in its deep part. 

 The laminar layer (Stratum lamellatum) is internal; it consists of the homy 

 laminae (Lamellae corneae), and is non-pigmented. The primary larninse are narrow 

 and thin at their origin at the lower margin of the coronary groove, but become wider 

 and thicker distally. At the junction of the wall and sole they are united by inter- 

 laminar horn to form the white line. Only the central part of the laminae becomes 

 fully keratinized. They are composed of non-tubular horn in the normal state. 



The sole consists of tubular and intertubular horn. The tubes run parallel 

 with those of the wall and vary much in size. 



The frog is composed of relatively soft horn, which is much more elastic than 

 that of the wall or sole, and is not fully keratinized. The horn tubes in it are slightly 

 flexuous. 



The hoof is non-vascular and receives its nutrition from the corium. It is 

 also destitute of nerves. 



THE CORIUM OF THE HOOF 



The coriiun of the hoof or pododerm (Corium ungulse) is the specially modified 

 and highly vascular part of the corium of the common integument which furnishes 

 nutrition to the hoof. It is convenient to divide it into five parts which nourish 

 corresponding parts of the hoof."^ 



1. The perioplic corium or ring (Margo corii ungulae) is a band 5 to 6 mm. 

 in width which lies in a groove between the periople and the coronary border of 

 the wall. It is continuous above with the corium of the skin, and is marked off by 

 a groove from the coronary corium. At the heels it widens and blends with the 

 corium of the frog. It bears very fine, short papillae which curve downward and 

 are received in depressions of the periople, to which it supplies nutrition. 



2. The coronary corium (Corium coronarium) is the thick part of the corium 

 which occupies the coronary groove, and furnishes nutrition to the bulk of the wall. 

 It diminishes in \tddth and thickness posteriorly, a,nd along the upper border of the 

 bar it is not clearly defined from the corium of the frog. The convex superficial 

 surface is thickly covered with filiform papillae 4 to 6 mm. in length, which are re- 

 ceived into the funnel-like openings of the coronary groove. At the heels and along 

 the bars the papillae are arranged in rows, separated by fine furrows. The deep 

 surface is attached to the extensor tendon and the cartilages of the third phalanx 

 by an abundant subcutis which contains many elastic fibers and a rich venous 

 plexus. 



3. The laminar corium (Corium' lamellatum) bears primary and secondary 

 laminae which are interleavetl with the horny laminae of the wall and bars in the 

 natural state. ^ It is attached to the dorsal surface of the third phalanx by a modi- 

 fied periostemn (Stratum periosteale) which contains a close-meshed network of 

 vessels, and to the lower part of the cartilages by a subcutis which contains a rich 

 venous plexus. The laminae are small at their origin above, become wider below, 

 and end in several papillae 4 to 5 mm. in length. They supply nutrition to the horny 

 laminae and to the interlaminar horn of the white line. 



4. The corium of the sole (Corium basilare) — also termed the sensitive sole — 

 corresponds to the horny sole, to which it supplies nutrition. It is often more or 

 less pigmented and bears long papillae, which are specially large along the convex 



1 In some veterinary works the statement is made that the various parts of the corium "se- 

 crete" corresponding parts of the hoof. The statement is, of course, ludicrous, as the relationship 

 here, both anatomically and physiologically, is the same as in the case of the corium and epidermis 

 of the skin. Hence the terms " keratogenous membrane" and "matrix" should be dropped. 



^ The laminae of the corium are commonly termed "sensitive" laminae to distinguish them 

 from the "homy" laminge, which are, of course, insensitive. 



