.' / 



THE HOKNY FKOG AND BULBS. 89 



than above. Behind, its upper border is comparatively sharp 

 ^nd straight, but as it advances and descends becomes flattened, 

 at length being lost at the bottom of the depression. 



As the periople, with its posterior expansion, the horny bulbs, 

 is united at either side with the frog-stay, and extends upwards 

 into the cleft of the frog, it forms at the back of the hoof two 

 shallow basin-like concavities, occupied by the rounded extremi- 

 ties of the plantar cushion (compare with horny bulbs, page 79). 



The entire upper surface of the horny frog is permeated 

 with small openings for the reception of the papillae which 

 secrete the horn of the froc?. The under surface of the hornv 

 frog (figs. 45 and 46), which 

 in the normal condition lies 

 in the same plane with the 

 bearing surface of the wall, 

 is broadest behind and 

 draws to a point in front. 

 At its posterior part, corre- 

 spondincr to the frog-stay 



^ . . Fig. 55.— Vertical mesial section of horny frog. a. 



above, is a depression, the npper surface; ft, frog-stay, (■,cleft of frog, show- 



ing at c' overlapping layers of horn. 



lurrow or median lacuna of 



the frog (figs. 45, 46, and 55, c). The portions of the frog, 

 bounding tliis furrow on either side, are termed its limbs (i). 

 The upper portions of the lateral surfaces (fig. 54, d) are united 

 with the upper and inner surface of the bars and with the sole 

 {compare with fig. 47, ci), the lower portions are free, and, aided 

 by the corresponding inner surface of the bar, enclose a furrow 

 termed the lateral furrow or lateral lacuna of the frog (figs. 45 

 and 46, m). 



As the horn of the frog grows obliquely downwards and 

 forwards, the antero-inferior extremity reaches further forward 

 than the antero-superior (figs. 54, c, and'55). The posterior end 

 •or base of the frog is its broadest part. It is formed by the 

 limbs of the frog, which here unite with the horny bulbs (figs. 45 

 ■and 46, Ick). At this point also the well-marked perioplic horn 

 -covering the heel- wall becomes continuous with the horny frog. 



