670 



A MANUAL OF VETERINARY PHYSIOLOGY 



practical application of this fact in the care and management of 

 the feet is very obvious. 



If a portion of horn be examined microscopically, it is found 

 that the compressed epithelial structure is tunnelled in such a way 

 as to form canals or tubes, or, at any rate, to form a structure 

 which is tube-like in nature (Fig. 235) . These tubes exist wherever the 

 growing surface is invested with papillae, so that where the papillae are 

 numerous the tubes are numerous, where they are absent the tubes 

 are absent. The only horny structures not secreted from a papillated 



b, c, The outer, middle, and 

 inner portions of the wall, 

 showing the canal system with 

 the tubular and intertubular 

 horn ; d, the horn laminae 

 bearing on their side the 

 lamellae, shown black : there 

 are sometimes a few short 

 laminae to be seen — one is 

 shown in the figure ; e, the 

 sublaminal tissue, from which 

 the sensitive laminae may be 

 seen dovetailed between the 

 horn laminae, and from the 

 sides of which the sensitive 

 lamellae grow. 



Fig. 235. 



-Horizontal Section of the Horn and Vascular Wall 

 of the Horse's Foot. Low Magnification. 



surface are the horn laminae, and consequently in these there are no 

 horn tubes ; everywhere else the horn is found to possess a more or 

 less tubular structure. The method of tube formation is simple. 

 The papillae growing from the various secreting surfaces are lodged 

 in canals in the horn. As the horn grows down from the surface 

 which secretes it, the canal enclosing the papilla gradually slides off, 

 but throughout the length of the horn a tubular appearance indicates 

 where the papilla was at one time lodged, and the cells of these tubes, 

 from their reaction with carmine, prove themselves to be different to 

 true horny structure. 



The horn which is secreted in the foot is therefore formed (1) from 



