THE APPENDAGES OF THE SKIN. 



919 



Id a transverse section of tlie wall, there are observed around the tubes, in 

 the intertnbular substance, as well as in the horny lamina?, small irre<;ulurly 

 elliptical spaces containing a solid denticulated mass of a brownish tint, which is 

 easily stained with carmine. These bodies are more elongated in the inter- 

 tnbular substance than in the walls of the tubes, and have a certain resemblance 

 to the cartilaginous capsules, but especially to the bone cavities filled by their 

 contents. 



Independently of the hard, dry, and flattened cells, there is found an opaque 

 substance that partly tills the tubes, and which is also sometimes met with in 

 their walls. This material does not differ from the last in its nature ; it is also 

 formed, as has been asserted by Gourdon and Ercolaui, of irregular granular 

 cells which are stained by the carminate ofammonia. 



Figment-corpuscles are found in the substance of the coloured horn, and are 

 disposed singly, or in small masses, in the epithelial cells of the inter-tubular 



Fig. 500. 



Fig. 501. 



f'/J 



HORN-CEI.L-S FROM THK SOLE 

 OF THK HOOF. 



a, Youug cells from the upper 

 surface of the sole ; b, cells 

 from the lower surface, or 

 dead horn of the sole. 



CONSTITUENT ELEMENTS 

 OF THE WALL. 



a, Horn-cell.s ; 5, horn- 

 fibre from the hoof of a 

 new-born foal, showing 

 the vertical dispositioa 

 of the cells. 



substance. The presence of these corpuscles has been denied, and the coloration 

 has been attributed to a greater condensation, at certain points, of the epithelial 

 elements. Fine pigment-granules are disseminated in the cells, but it is evident 

 that beyond these there are at different points pigment-corpuscles ; for, after 

 treating a section of coloured horn with soda, the epithelial elements are distended, 

 become pale, and disappear, leaving, however, here and there, masses of black 

 granulations. These pigmentary corpuscles are absent in white horn. 



Development of the Hoof. — The hoof being a dependency of the epidermis, 

 is developed like it — that is, by the incessant formation of cells in the layer that 

 corresponds to the stratum mucosima. The velvety tissue fonns the sole and 

 frog ; the perioplic ring the periople, and the coronary cushion the wall. In 

 these different parts, the epithelial cells multiply, and become flattened in layers 

 parallel to the surface that secretes them, and in proportion as they recede from 



