THE SKIN. 355 



surface between the bases of these papillae. Frag- 

 ments of epithelial cells may usually be found in the 

 lumen of these tubes. 



The laminae just described provide an enormous 

 surface of contact between the inner face of the wall 

 and the external surface of the pedal bone. It is 

 estimated that this surface is equal in area to eight 

 or ten square feet in each hoof, and its chief function 

 is doubtless to furnish support to the body weight 

 of the horse. The sensitive laminae thus act as an 

 extensive and delicate cushion, tempering the jar 

 sustained in walking or running. An inflammation 

 of the sensitive laminae is known as laminitis, a 

 malady not uncommon in the horse. 



The normal growth of the hoof is estimated at nearly 

 one-half inch a month. Just how the horny laminae 

 move imperceptibly downward past the softer lami- 

 nated structure is a subject of much speculation among 

 veterinarians, but one on which opinions differ. It 

 seems to me any sliding process is difficult to explain 

 and that the solution sought is one of cell growth. 

 During embryonic development it is easy to conceive 

 of a rapid multiplication of the germinal epithelium, 

 that is, the cells that form the membrane clothing the 

 insensitive laminae. Such a growth produces lateral 

 pressure and accounts for the extensive folding of these 

 laminated structures. In the adult foot the cells of 

 the germinal layer show nuclei rich in chromatin, 

 and being epithelial cells their multiplication con- 

 tinues through life. The horny laminae, lying exter- 

 nal to this layer, doubtless owe their origin, as well 

 as their constant and regular growth, to the cells of 



