THE APPENDAGES OF TEE SKIN. 917 



closely, at their upper third, to the external side of the bars, and anteriorly to the 

 inner border of the sole. " This union is so close that no line of demarcation is 

 apparent between these parts, and their separation can only be obtained by pro- 

 longed maceration. The non-adherent, or free portion, forms the inner side of 

 the cavities know as the lateral lacmiie, or commissures of the frog, whose external 

 side is constituted by the inft-rior face of the bai-s" (Bouley). 



The superior plane, forming the internal fju-e of the frog, is cribbled with 

 holes like that of the sole, and is exactly moulded on the pyramidal body of 

 the plantar cushion. It also offers a triangular excavation, di\ided posteriorly 

 into two latter channels by a prominence directed from before backwards, to 

 which Hracy Clark gave the name of froy-staij, but which M. Bouley prefers to 

 designate the stay {arete — spine or ridge) of the frog. 



The base or posterior extremity of the frog, constituted by the extremities of 

 its branches, forms two rounded, flexible, and elastic eminences separated from 

 each other by the median lacuna : they cover the angles of inflection of the wall, 

 and are continuous at this point with the perioplic band. Bracy Clark named 

 them the glomes of the frog. 



With regard to the summit — or anterior extremity of the organ — it is a point 

 wedged in the re-entering angle comprised between the two portions of the inner 

 border of the sole. 



In the Ass and Mule, the hoof is always naiTower, laterally, than that of the 

 horse ; the wall is always higher and thicker, the sole more concave, the frog 

 smaller and deeper seated at the bottom of the excavation formed by the sole, 

 and the horn is much more hard and resisting.^ 



(The angle of the wall of the hoof in front varies from 50° to 56°, though 

 usually erroneously stated to be 45°. The inner face of the wall — at tlie middle 

 of the toe, and in a line with the frog-stay — frequently shows a more or less salient 

 and conical prominence — base towards the lower margin of the wall — which 

 corresponds to a vertical depression in the os pedis. Vallada imagined that this 

 projection served to unite the wall and sole more closely ;; but it is far more pro- 

 bable that its function is the same as that of the frog-stay — to maintain the 

 position of the os pedis, and prevent its rotation within the hoof. I have, there- 

 fore, named it the " toe-stay.") 



Structure of the Hoof-horn. — The structure of the horn has been the 

 subject of a great number of researches ; Gurlt, Delafond, Bouley, (bourdon, and 

 Ercolani '^ have given descriptions of it, and we have also some details to add to 

 the labours of these authorities. 



The horny substance constituting the hoof of Solipeds, has a fibrous appearance ; 

 this is most conspicuous in the wall, less apparent in the frog and deeper portions 

 of the sole, but impossible to distinguish in the superficial layer of the latter, 

 where the disintegration continually taking place separates the horn in scaly 

 fragments of varying thickness and extent. The consistence of the horn is 

 always less in the frog than in the sole and wall. Its tint is in some hoofs black, 

 in others white, and in others, again, a mixture of these two. The inner face of 

 the wall, however, is never black ; and when the lower part of the limb is partially 



* The third phalanx of the anterior limb of these animals has the same shape as in the 

 Horse, notwithstanding the lateral flattening of the hoof covering it. 



* (The researches of Professor Eawitsch must be omitted. They will be found in vol. 

 xxviii. of the Mafjazin fur Tliierhetlkunde, and also in a little brochure entitled Ueher den 

 feineren Bau und das Wnehdhum des Eufhorns—BerMu : 18(j3. Leiseiing must likewise be 

 referred to. My own researrh' s are published in the Veterinarian for 1871.^ 



