88 



THE PEOTECTIVE STRUCTURES OF THE FOOT. 



3. The Horny Frog. 

 ' (Figs. 35, 45, 46, 48, 54, and 55.) 



The horny frog exhibits, in general, the form of the plantar 

 cushion, or more precisely the sensitive frog on which it is 

 moulded. Considered as a whole, it resembles a four-sided 

 pyramid lying on one face, and thrust like a wedge into the 

 triangular space l:)Ounded by the bars and sole at the back of 

 the under surface of the hoof. The horn of the frog is soft, 



resembling that of the periople, 

 is very elastic, and has been 

 compared with india-rubber. 

 In spite of its softness and the 

 readiness with which it may 

 be cut, it possesses considerable 

 tenacity, and does not break 

 like that of the sole, but tears 

 away in shreds or larger masses. 

 The horny frog presents four 



Fig. 54.— Horny frog removed from hoof, to- SUrfaCCS and tWO extrCmitlCS. 

 getherwith the periople and the expansion rni ,,^,~.p,, qnrfqpp whiVh onlv 

 of tlie latter wliich covers tlie wall, o, de- J-UC UppCl bUliace, WniGU Oni} 



pression divided into two by 6, the frog- ljpp^i^-,pc. vim'hlp nffp7- VPninval of 

 stay ; c, portion of the horny frog which 'Jecomes Vlbl UlC til LCI IcmoVcii UL 



unites with the bars; d, portion of frog ^i hnnf ic: an a^r-Aof ihmicrh 



which above is in contact with the bar, but ^^^^ nOOI, LS dU eXdCL lUOUgll 



below, at (f, appears as a free surface ;e, ^pvprsipd VPl^vnflllPt.inTl of the 

 point of frog: /, periople; /, perioplic iCVeibCU ILpiUUUCblOIl Ui LlltJ 



sheath of wall. plantar cushion, to which it 



stands in the same relation as does an impression to the seal 

 producing it. It, therefore, resembles an elongated, triangular, 

 ilattish furrow (figs. 54, a, and 48, m), bounded by two lateral 

 surfaces running obliquely downwards and towards the middle 

 line (figs. 54, c, and 48, k), the whole fitting into the space 

 between the bars. At the back of this depression and in the 

 centre line rises a well-marked prominence, overtopping, more 

 or less, the upper margins of the bars, and dividing the depres- 

 sion into two equal parts (fig. 48, m). It is called the frog-stay 

 (figs. 35, hy 48, /, and 54, h), and exactly corresponds with the 

 depression on the under surface of the plantar cushion into 

 which it fits. 



The two lateral surfaces of the frog-stay run obliquely down- 

 wards and outwards, and the part is, therefore, thicker below 



