DISSECTION OP THE ANTERIOR LIMB. 37 



the sole presents a convex border, which unites it intimately to the 

 lower border of the wall, a line of whitish horn marking the junction of 

 the two strvxctures. Posteriorly it has a deep V shaped indentation, 

 into the central point of which the frog penetrates, while behind that on 

 each side it is related to the bar. 



The sole of the hind hoof is distinguished from that of the fore by 



being more vaulted, and by being more pointed (less circular) at the toe, 



this latter difference affecting also the form of the wall in the same 



region. The outer edge of the sole is more convex than the inner, 



• which enables one to readily distinguish between a right and a left hoof. 



The Fbog. This is a distinctly elastic mass of horn which, in a stato. 

 of nature, projects sufficiently to come into contact with the ground, 

 and thus give the animal a secure foothold. Its inferior surface shows 

 posteriorly a shallow cleft, or depression, termed the median lacuna. 

 The lateral lacance lie at the sides of the frog, the outer boundary of 

 each lacuna being formed by the bar. The superior surface shows, 

 vertically over the median lacuna, a projection termed the frog-stay. 

 On each side of the frog-stay this surface is depressed, and the whole is 

 moulded on the plantar cushion. This surface is puuctatfrt^-and +hp 

 papillse of the plantar cushion are received into the minute apertures. 

 The posterior extremity, or base, of the frog consists of two rounded emi- 

 nences — the hulhs, or glomes- — separated from each other by the median 

 lacuna. The anterior extremity, or point, is wedged into the centre of the 

 sole. The lateral borders bring the frog into relation with the bars and 

 the sole, and there is an intimate union with each of these at the point 

 of contact. 



^iIiNUTB Structure of the hoof. The entire hoof is an aggregation . 

 modified epithelial cells, which here represent the homy layer of the 

 epidermis. When a thin section across the wall, sole, or frog is 

 examined, the horn substance is seen to be arranged in the form 

 [of tubes, cemented together by an intertubular substance, and 

 sontaining within their lumen a quantity of intratubular material. 

 Ul of these— tubular, intertubular, and intratubular— are composed of 

 Lodified epithelial cells, differing in the three situations in the direction 

 If the cells, their state of aggregation, or the presence or absence of 

 |ontained pigment. The tubes of the wall are straight, and extend 

 parallel to the surface, from the coronary to the inferior edge of the^ 

 wall. The tubes of the sole have the same disposition, but those of- the 

 frog are slightly flexuous. The upper end of each tube is occupied by 

 an elongated vascular papilla, which belongs, in the case of ifhe wall, to 

 the coronary cushion; in the periople, to the perioplic ring; and in 

 the sole and frog, to the sensitive structures of the same' names. In the 

 growing hoof the bond of connection between thepe papillated surfaces 

 (which represent the corium of the skin) and the corresponding part of 



