154 ZOOTOMY. 



by five clawed digits ; of these the first is the shortest, 

 the second and fifth are of nearly equal length ; the fifth, 

 however, being the slenderer, and appearing shorter from 

 the fact that it arises nearer the proximal extremity of 

 the hand ; the third is considerably longer than the second, 

 and the fourth slightly longer than the third (cf. §§ 107 



-115)- 



119. The large mouth, the gape beginning at the end of 



the snout and extending backwards nearly to the auditory 

 apertures (§ 122). 



120. The nostrils, or anterior nares, small, rounded 

 apertures, situated one on each side of the snout, a short 

 distance from its anterior end. 



121. The eyes, situated one on each side of the head, 

 about midway between the corresponding nostril and 

 auditory aperture (§ 122) : each is guarded by a short, thick 

 upper eyelid, and a deep, thin lower eyelid, which, 

 when the eye is closed, covers the greater part of it : within 

 the eyelids is the thin, transparent nictitating membrane, 

 which springs from the anterior corner of the eye and shuts 

 backwards over the eye-ball. 



122. The auditory aperture, situated a little posterior 

 to the extremity of the gape, and nearly as large as the 

 exposed portion of the eye : stretched over it, a little below 

 the general level of the head, is the thin tympanic 

 membrane. 



123. The vent, or cloacal aperture (Fig. 39, d), a 

 large transverse cleft at the root of the tail. 



124. The exoskeleton, consisting of a closely-fitting 

 armour of epidermic scales : those on the dorsal surface 

 of the trunk are small, hexagonal in outline, and indistinctly 

 keeled ; on the ventral surface they are large and are arranged 

 in eight longitudinal series ; forming the anterior edge of the 



