planta,) of the tarsus is frequently clothed with very thickly set short hairs, forming a covering, which has been called the foot-cushion, (pulvillus). Other peculiarities connected with this section of the leg will appear when we come to examine it in the different orders. The number of the joints has been found to afford very convenient means for forming sub-divisions in the several primary sections, as they are ascertained to be pretty uniform in nearly allied species. Such as possess five joints in all the tarsi are called pentamerous; those having five joints in the fore and middle legs, but only four in the hinder pair, heteromerous; when all the tarsi are four jointed, tetramerous; three jointed, trimerous; two jointed, dimerous; and lastly, such as have only one joint are termed monomerous.
Owing to the fore legs frequently presenting a structure different from the rest, adapting them for becoming instruments of prehension, Mr. Kirby thought they made so near an approach to arms, that he applied to them that name. The five portions described above, would, in this view, be regarded as analogous to the clavicle, scapula, humerus, cubitus, and hand. Although many remarkable appearances might be cited in support of this view, yet it is obvious that the primary use of these limbs as instruments of motion is never superseded, and we are not entitled to bestow a new name on an organ merely on account of a few slight modifications of structure, or because it has been made subservient to certain additional uses. It is not, besides, in all cases the fore legs that supply the place of arms; in
