6 THE FROG CHAP. 



of about the same length as the third. All the toes are 

 joined together by thin transparent webs, and, like the 

 fingers, have no nails. The name digit is conveniently 

 applied both to fingers and toes. Between the bases of 

 the thighs, at the hinder end of the trunk, is a small 

 aperture, the vent or anus. 



In the squatting posture the body is raised upon the 

 arms, which are kept slightly bent at the elbows, with the 

 fingers spread out and directed forwards. In this position 

 the innermost of the four fingers correspond with our own 

 index-finger, the frog having no thumb. The hind-limb, 

 under similar circumstances, is bent into a sort of Z, the 

 knee being directed forwards and the ankle-joint backwards. 

 The toes are turned forwards, and the inner one, which is 

 the smallest of all, corresponds with our own great toe. 



Owing to the bent position of the limbs, we cannot very 

 well, as in our own arms and legs, speak of their upper and 

 lower ends. It is therefore customary to call the end of a 

 limb, or of any division of a limb, which is nearest to the 

 trunk, the proximal end, that which is furthest away the 

 distal end. Thus the proximal end of the fore-arm is the 

 elbow region, the distal end of a digit is its tip. 



The whole body, including head, trunk, and limbs, is 

 covered with a soft, slimy skin, of a brown colour, irre- 

 gularly spotted with brown or black on the upper or dorsal 

 surface, and whitish on the under or ventral surface. The 

 colouring is, however, not constant ; in a frog kept in the 

 dark the black spots increase to such an extent that the 

 whole animal becomes almost black, while if kept in full 

 daylight a corresponding brightening of the tints takes 

 place. Moreover, the spots and patches of brighter colour 

 are very variable : if you examine a dozen specimens you 

 will see at once that no two are alike in this respect. The 



