PLANTAR SYSTEM. 429 



to which it is intimately united by horny matter, the two toge- 

 ther forming a stout bulwark of defence to those parts of the 

 internal foot included between them. — The points or heels are 

 the two posterior salient angles received into the angular inter- 

 vals between the outer and inner walls or bars. Although, 

 naturally, the least exposed, these are the parts most subject 

 to injury or pressure from the shoe, being the seat of that disease 

 mistakenly called corn. — The middle or centre of the sole is 

 the portion more immediately surrounding the fore parts of the 

 frog, and would (were the sole a regular arch) be the most ele- 

 vated part ; but, in general, we find the sole flattened hereabouts : 

 the highest parts of the arch being the angles alongside of the 

 bars ; the lowermost, those around the toe. 



Surfaces. — Of the surfaces, the superior (as was mentioned 

 before) is unevenly convex ; the inferior, correspondently con- 

 cave. The former is everywhere pitted, particularly about the 

 heels, with numerous circular pores, running in an oblique direc- 

 tion, the marks of which remain evident upon the inferior surface 

 hkewise. These pores are the impressions made in the soft horn 

 by the villi of the sensitive sole, from whose orifices the horny 

 Hjatter is produced. They also form the bond of union between 

 the horny and the sensitive soles : which is of a nature so strong 

 and resisting, that it requires the whole strength of a man's arm 

 to effect their separation — an operation of a cruel description 

 that was wont to be practised in times past, under the fallacious 

 notion that " drawing the sole" was extirpating the malady. 



Thickness. — The natural thickness of the sole may be estimated 

 at about one-sixth of an inch. There will be found, however, 

 variations from this standard in different horses ; and it will 

 also very much depend on the part selected for measurement. 

 The portion of the sole most elevated from the ground — that 

 which forms a union with the bars — is nearly double the thick- 

 ness of the central or circumferent parts ; and next to this, in 

 substance, comes the heel. I do not find that the sole " grows 

 thinner from the circumference to the centre," as has been stated 

 by an author of celebrity. 



The Ff 



og. 



The frog is the prominent, triangular, spongy body, occupying 

 the chasm l^ft by the inflection of the bars. 



Situation and Connexion. — The frog is fitted into the interval 

 between the bars ; the three, altogether, filling up the vacuity 

 in the sole, and thereby completing the circle, and establishing 

 the solidungulous character of the foot. The frog extends for- 

 ward, towards the toe, about two-thirds of the longitudinal 



