HOKN. 517 



site sense, lying flat on each other at right angles with the 

 fibres. This dense bed of cells forms the bond of union be- 

 tween the fibres, which become loose and detached from 

 each other when the horn bj~ accumulation is removed 

 from its proximity to the source of production, and its inte- 

 gral strength is lost. 



The fibres, we have said, are formed from the papillae, but 

 the cells of the material which joins them are produced from 

 the surface between the papillae and the deeper layers from 

 the surface of the laminae or podophylla. Thus the horn 

 fibres descend over the laminae, and are attached to these by 

 cells constantly developed, and which act as the agglutinating 

 material. 



The pigment which colours all dark horn is disposed irre- 

 gularly between the cells of the fibres, as in the case of hair, 

 and has no very regular disposition. 



The difference between the horn of different parts of the 

 horse's hoof depends not a little on the relative amount of 

 fibres and inter-fibrous substance. The horn of the wall is 

 tough, and breaks up into fibres as it grows beyond a natural 

 length. This is due to the toughness acquired by the fibres 

 in their lengthy course, and to the crumbling of the cells be- 

 tween them as mentioned above. The horn of the sole is 

 detached in flakes, and this depends on the fact that the 

 fibres are short, do not pass over or into a bed of agglutinat- 

 ing material, and when at a certain distance from the papillae 

 whence they originate, they break off. Flakes are thus de- 

 tached from the frog. The growth of horn is unlimited, and 

 in the case of the horse's hoof, we find that if, from the feet 

 being protected by an iron shoe, when injudiciously managed, 

 whether through want of exercise and proper ground to 

 move on, certain parts are allowed to grow beyond the 

 natural depth which would not occur if the animal was free 



