THE HOOF 891 
ridge formed by the junction of the frog with the bar and sole. This surface 
presents fine striz and openings for the papillse of the corium. The external or 
ground 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 Fic. 714.—Section oF Hoor or Horse. 
is composed of epithelial cells which The section is cut just above the ridges of the frog and 
3 we b . bars and parallel with the ground surface. 17, Wall; 2, sole; 
are more or less completely keratin-  ° ais a ease i 
¥ 5, spine of frog or ‘‘frog-stay"’; 4, ndge formed by Junction 
ized except in its deepest part, the of frog and bar; 4, central furrow over apex of frog; 6, 
stratum germinativum ; here the cells 8mm of wall; 7, lamin of bar. 
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 wall 
may be regarded as consisting of 
three layers. The external layer 
consists of the periople and the 
stratum tectorrum. 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 
Fic. 715.—Frontat Section or Hoor or Horse, Posterior less than an inch wide, except at 
ee . arg me, ae 2 nae ie os. the heels, where it is much wider, 
eraisdre forhed by junction are and bar: 7, laminw of 2@2d caps the angle of inflection of 
bar; 8, lamin of wall; 9, coronary groove; 10, periople of heel. 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 medium) forms the bulk of the wall, and 
