GENERAL OBSERVATIONS 51 



aspects, giving a section of a lamina the appearance of 

 being studded with papillae. We have already pointed out 

 the ridge-like formation of the human nail-bed, and noted 

 that, with the exception that the secondary ridges are not 

 so pronounced, it is an exact prototype of the laminal 

 formation of the corium of the horse's foot. 



The distribution of the laminae over the foot we have 

 discussed in the chapter devoted to the grosser anatomy. 

 In a macerated foot the sensitive laminae of the corium 

 interdigitate with the horny laminae of the hoof ; that is 

 to say, there is no union between the two, for the simple 

 reason that it has been destroyed; they simply interlock 

 like the unglued junction of a finely dovetailed piece of 

 joinery. But no further, however, than the irregularities 

 of the underneath surface of the epidermis of the skin can 

 be said to interlock with the papillae of the corium does 

 interlocking of the horny and sensitive laminae occur. It 

 is only apparent. The horny laminae are simply beauti- 

 fully regular epidermal ingrowths cutting up the corium 

 into minute leaf -like projections. 



In a macerated specimen, then, the exposed sensitive 

 structures of the foot exhibit the corium as ( 1 ) the Coro- 

 nary Cushion, fitting into the cutigeral groove; (2) the 

 Sensitive Lamina, clothing the outer surface of the ter- 

 minal phalanx, and extending to the bars; (3) the Plantar 

 Cushion, or sensitive frog; and (4) the Sensitive Sole. 



The main portion of the wall is developed from the 

 numerous papillae covering the corium of the coronary 

 cushion. We have in this way numberless down-growing 

 tubes of horn. Professor Mettam describes their formation 

 in a singularly happy fashion : 'Let the human fingers 

 represent the coronary papillae, the tips of the fingers the 

 summits of the papillae, and the folds of skin passing from 

 linger to finger in the metacarpophalangeal region the 

 depressions between the papillae. Imagine that all have a 

 continuous covering of a proliferating epithelium. Then 

 we shall have a more or less continuous column of cells 

 growing from the tip of the finger or papilla (a hollow tube 



