THE HOOF 



891 



ndge formed by the junction of the frog with the bar and sole. This surface 

 presents fine striae and openings for the papillae of the corium. The external or 

 grotand surface presents a central 

 sulcus (Sulcus cunei), which is 

 bounded by two ridges or crura 

 (Crura cunei). The medial and lat- 

 eral surfaces (Facies medialis et lat- 

 eralis) are united at the upper part 

 with the bars and sole, but are free 

 below and form the central wall of 

 the deep collateral sulci (Sulci para- 

 cuneati), which are bounded out- 

 wardly by the bars. The base (Basis 

 cunei) is depressed centrally and 

 prominent at the sides, where it 

 unites with the angles of the wall; 

 the junction here is covered by the 

 expanded periople and constitutes 

 the bulb of the hoof (Pulvinus digi- 

 talis). The apex (Apex cunei) oc- 

 cupies the central angle of the con- 

 cave border of the sole, and forms a 

 blunt, round prominence a little in 

 front of the middle of the ground sur- 

 face of the hoof. 



Structure of the Hoof. — The hoof 

 is composed of epithelial cells which 

 are more or less completeljr keratin- 

 ized except in its deepest part, the 

 stratvun germinativum ; here the cells 

 have not undergone cornification, and 

 by their proliferation maintain the growth of the hoof. The cells are in part 

 arranged to form tubes (Cylindri cornei) which are united by intertubular epi- 

 thelium, and enclose medullary 

 cells and air-spaces. The waU 

 may be regarded as consisting of 

 three layers. The external layer 

 consists of the periople and the 

 stratum tectorium. The periople 

 is composed of soft, non-pig- 

 mented, tubular horn, and be- 

 comes white when the hoof is 

 soaked in water. It is contin- 

 uous with the epidermis of the 

 skin above, and extends down- 

 ward a variable distance. Usually 

 it forms a distinct band somewhat 

 less than an inch wide, except at 

 the heels, where it is much wider, 

 and caps the angle of inflection of 

 the wall. The stratum tectorium 

 is a thin layer of horny scales 

 which gives the outer surface of the wall below the periople its smooth, glossy ap- 

 pearance. The middle layer (Stratum coronarium) forms the bulk of the wall, and 



Fig. 714. — Section of Hoop of Horse. 

 The section is cut just above the ridges of the frog and 

 bars and parallel with the ground surface. 1, Wall; S, sole; 

 3, spine of frog or "frog-stay"; 4. ridge formed hy junction 

 of frog and bar; 5, central furrow over apex of frog; (?, 

 laminse of wall; 7, laminse of bar. 



Fig. 715. — Frontal Section of Hoof of Horse, Posterior 



Part Viewed from in Front. 



1, Wall; 2, sole; 3, bar; 4, frog; B, central ridge of frog; 8, 



lateral ridge formed by junction of frog and bar; 7, laminge of 



bar; S, laminse of wall; 9, coronary groove; 10, periople of heel. 



