THE INTEGUMENTARY APPENDAGES. 



809 



Fig. 377. 



canals are not empty for the remainder of their extent ; bufc contain a 

 particular white substance, which is so opaque that it appears of a fine 

 black hue when examined as a transparency in the microscope. This matter 

 is not deposited in a uniform manner in the canals, but irregularly-looking, 

 like a knotted cord or a necklet of beads ; and, where it does exist, it 

 does not always exactly fill the calibre of the tube, an interval being 

 observed between the inner face of the latter and the intratubular deposit. 

 Sometimes it is seen without the canals, among their concentric lamellae, 

 and even in the horny intertubular substance. 



If we are desirous of completing our knowledge of the minute organ- 

 isation of the hoof-horn by studying the anatomical elements constituting 

 it, we will find that it is formed of epithelial cells belonging to the kind 

 most wide-spread in the economy pavement epithelium. These horn 

 epithelial cells are very thin, pale, polygonal, and generally oblong, have 

 sharply defined borders and finely granular faces, sometimes showing a 

 nucleus containing a single or .multiple nucleolus. The nuclei sometimes 

 occupy the centre, at other times another part of 

 the cells even their margins ; and they also con- 

 tain pigment granules more or less coloured and 

 numerous. Acetic acid acts very slowly on them, 

 and is limited to making them more transparent. 

 Potass and soda at first softens, then distends 

 them, causing their granulated aspect to disappear, 

 and rounding their contours ; afterwards, they be- 

 come quite diaphanous, and finish by being com- 

 pletely dissolved. 



Examined in their reciprocal relations, these 

 epithelial cells are not seen to be agglomerated 

 confusedly together, but are, on the contrary, dis- 

 posed in a regular manner, forming a real frame- 

 work that wonderfully concurs in assuring solidity 

 and flexibility. In the walls of the tubes we see 

 them arranged horizontally around the canal, and HORN-CELLS FROM THE SOLE 

 stratified from within to without, so as to form OF THE HOOF - 



successive concentric layers. In the intertubular a > Youn S cells from the upper 

 horn they are disposed differently, their stratifi- 

 cation being no longer parallel to the direction of 

 the tubes, but perpendicular to it, and piled upon 

 each other in the intervals separating the latter. This change of direction 

 does not occur suddenly; at the limits of the tubes epithelial cells are 

 seen lying obliquely. 



In a transverse section of the wall, there are observed around the tubes, 

 in the intertubular substance, as well as in the horny laminae, small 

 irregularly elliptical spaces containing a solid denticulated mass of a 

 brownish tint, which is easily stained with carmine. These bodies are 

 more elongated in the intertubular 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 fills 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 Ercolani, of 

 irregular granular cells which are stained by the carminate of ammonia. 



surface of the sole ; 6, Cells 

 from the lower surface, or 

 dead horn of the sole. 



