XIII.] THE FROG. 153 



behind the eyes, which is very characteristic of the species. 

 The coloration of different frogs of the same species differs 

 widely; and the same frog will be found to change its colour, 

 becoming dark in a dark place, and light if exposed to the 

 light. 



The body of the Frog presents only two median aper- 

 tures, the wide mouth and the small cloacal aperture. The 

 latter is situated at the posterior end of the body, but rather 

 on its upper side than at its actual termination. It is 

 commonly termed the anus, but it must be recollected that 

 it does not exactly correspond with the aperture so termed 

 in the Mammalia. 



The two nostrils, or external nares, are seen at some dis- 

 tance from one another iipon the dorsal aspect of the head, 

 between the eyes and its anterior contour. The eyes are 

 large and projecting, with well-developed lids, which shut 

 over them when they are retracted; and, behind the eye, 

 on each side of the head, there is a broad circular area 

 of integument, somewhat different in colour and texture 

 from that which surrounds it ; this is the outer layer of the 

 membrane of the tympanum, or drum of the ear. 



The fore-legs are very much shorter than the hind-legs. 

 Each fore-limb is divided into a hrachium, antebrachium and 

 maniis, which correspond with the arm, fore-arm and hand in 

 Man. The manus possesses four visible digits which answer 

 to the second, third, fourth, and fifth fingers in Man. There 

 is no web between the digits of the manus. 



The hind-legs are similarly marked out into three divi- 

 sions, femur, crus, and pes, of which the femur answers to 

 the thigh, the crus to the leg, and the pes to the foot, in 

 Man. The pes is remarkable not only for its great relative 

 size as a whole, but for the elongation of the region which 

 answers to the tarsus in Man. It will be observed, however, 

 that there is no projecting heel. There are five long and 



