PLANTAR SYSTEM. 431 



Mr. Clark to exhibit, in the natural foot at its full growth, "a 

 considerable bulbous enlargement," which, by way of distinction, 

 he calls the cnshion of the frog. On making a perpendicular 

 section of the foot, Mr, C. finds this part is situated " nearly 

 opposite or under the navicular bone." And it would appear (ac- 

 cording to this author) that this "rotundity, or swell of the 

 frog," is never reproduced after it has once been annihilated by 

 the knife of the smith. 



The superior Surface of the Frog, every where con- 

 tinuous, uniform, and porous, being the counterpart in form of 

 the inferior, presents us with nothing but reverses: where the 

 one is hollow or depressed the other rises into swells and emi- 

 nences, and vice versa. This accounts for our finding the part 

 opposite to the cleft elevated into a conspicuous eminence, 

 bounded on its sides by two deep channels, and a hollow of 

 broader but shallower dimensions in the front. To this central 

 conical elevation Mr. Clark has given the name of frog-stai/, 

 from some novel notions he entertains of its physiology. Such 

 a bold promontory of horn rising in the middle of iDroad and 

 deep channels is well calculated to form that dovetailed sort of 

 connexion with the sensitive foot, which greatly augments 

 their surfaces of apposition, and establishes their union beyond 

 all risk or possibility of dislocation. It is a part which (as far 

 as my observations on it have extended) grows and becomes 

 developed together with other parts of the foot ; and one that is 

 apt to vary in its relative volume in different feet. In front of 

 the frog-stay, the lateral borders, bounding the hollow in the 

 middle, describe a waving line, which, near half-way to the 

 point of the toe, exhibits a dip or depression: this marks the 

 impression of the navicular bone, and is the part immediately 

 opposite to the " cushion of the frog," — a coincidence important 

 to be borne in mind, as tending to throw some light on the nature 

 of this new-christened structure*. 



THE SIDES are the parts by which the frog establishes its 

 union with the borders of the triangular vacuity in the hoof into 

 which it is admitted. Along their superior borders they are 

 transversely lamellated, or rather indentated, in order that they 

 may be fitted to the internal surfaces of the bars, which exhibit 

 a similar structure. 



The Commissures are the two deep triangular-shaped hollows 

 between the bars and the sides of the frog. In being only the 

 superior borders of these parts that are engaged in their union ; 

 their broad unattached parts, below, form the boundary wails 



* In fact, the cushion of the frog appears to be nothing more than a bulge 

 of the part produced by the superincumbent pressure of the navicular bone. 



