Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget .. . the house-fly, already foot has five toes; all, except the thumb,terminated by a sharp curved claw. On theunder surface of each toe (represented in ) there are as many as sixteen transverseslits, leading to the same number of cavities, or sacs; these open for-wards, and their exter-nal edge is serratedappearing like the teethof a small-toothed section of the foot,showing these cavities,is seen in Fig. 212. Allthese parts, togetherwith the cavities, arecovered or
Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget .. . the house-fly, already foot has five toes; all, except the thumb,terminated by a sharp curved claw. On theunder surface of each toe (represented in ) there are as many as sixteen transverseslits, leading to the same number of cavities, or sacs; these open for-wards, and their exter-nal edge is serratedappearing like the teethof a small-toothed section of the foot,showing these cavities,is seen in Fig. 212. Allthese parts, togetherwith the cavities, arecovered or lined withcuticle. Below themare large muscles which draw down the claw ;and from the tendons of these muscles arise twosets of smaller muscles, situated so as to be putupon the stretch, when the former are in the contractions of these muscles, the orificesof the cavities, or sacs, to which they belong,are opened, and the serrated edges applied ac-curately to the surfaces with which the feet arein contact. Sir Everard Home, in his accountof this structure, compares it to the sucking disk. 462 THE MECHANK AL FUNCTIONS. of the Remora* By its means the animal isenabled to walk securely upon the smoothestsurfaces, even in opposition to the tendency ofgravity. It can run very quickly along thewalls or ceiling of a building, in situations whereit cannot be supported by the feet, but mustdepend altogether upon the suspension derivedfrom a succession of rapid and momentary ad-hesions. Although the Sauria are better formed forprogressive motion than any of the other ordersof reptiles, yet the greater shortness and obliqueposition of their limbs, compared with those ofmammiferous quadrupeds, obliges them in ge-neral to rest the weight of the trunk of the bodyon the ground, when they are not actuallymoving. None of these reptiles have any otherkind of pace than that of walking, or jumping;being incapable of performing either a trot or agallop, in consequence of the obliquity of
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