66 THE PKOTECTIVE STKUCTURES OF THE FOOT. 



directions, and passing through these alternating strata and at 

 rioht ancfles to them are the horn fibres. Such an arrancrement 

 must consolidate the whole structure and resist traction when 

 brought to bear in any direction, and that the toughness of the 

 horn of the frog is surprising anyone will admit who has 

 attempted to pull a piece away. 



The horny sole also is developed from cells covering the 

 papilla? of the sensitive sole, and from those covering the surface 

 of the corium between them. The papillae, however, are short, 

 and the amount of horn derived from other than a papillary 

 origin is relativelv abundant. The two factors taken in coniunc- 

 tion, the short tubes and the cellular horn, explain the lack of 

 colierence and the rapid exfoliation. Furtlier, there is no 

 natural secretion provided to keep the horn from rapidly 

 desiccating and crumbling, as in other regions, where, if no 

 secretion is provided, as in the frog, yet a thin protecting 

 pellicle descends over the nascent horn, prevents it from cracking 

 until it is sufficiently hard to withstand the usages to wdiich it 

 is put. The absence of secretion, or of periople, together with 

 alternations of excessive dryness or of moisture to which the 

 sole is subjected, accounts for the crumbling and breaking down 

 of the horny sole ; and, beyond this, it should be mentioned that 

 certain structures, as hairs, tend to break off and disintegrate 

 when they have reached a certain length, or, in other words, 

 have passed beyond the sphere of influence of the tissues from 

 which they have been derived. 



The perioplic horn is derived from the cells covering the 

 perioplic ring. Here, again, as in other regions, there are present 

 papilLT. The horn developed passes over and becomes super- 

 ficial to the horn derived from the coronary band, and its rela- 

 tion to the latter part of the hoof wall is like that of a varnish. 

 It has been termed, not inaptly, an epithelial varnish, and as such 

 it acts. The newly-formed horn from the coronary band when 

 submitted, as it sometimes unwittingly is, to desiccation, cracks ; 

 and, according to the extent of the crack, a lesion serious or not 

 may arise, but fissures in the horny capsule are rarely seen, un- 

 less of traumatic or of violent origin, if the periople is still in- 

 tact ; and, doubtless, many cases of so-called brittle feet are due 

 to a deficiency of secretion from the perioplic ring. The periople 

 passes down over the wall as a thin pellicle of horn, and may be 



