260 



AMPHIBIANS. 



but imbibe moisture through the pores of their integument. Moisture is, indeed, 

 essential to their existence, and if they be confined in a dry atmosphere they 

 soon perish. It is true that frogs may be seen basking in the sun's rays, and 

 apparently enjoying the warmth as much as lizards, but they only do this in the 

 neighbourhood of water, to which they retire when necessary. Such members of 

 the class as inhabit dry localities, are mostly nocturnal, avoiding sunshine, and 

 wandering abroad when they can obtain moisture from dew, 



The skeleton of the Amphibians presents many peculiarities, and 

 in some forms has numerous fish-like characters. For instance, in 

 certain of the forms with permanent gills the vertebrae are scarcely distinguishable 

 from those of fishes ; whereas in the true newts they have a rounded knob at the 

 front of the body and a cup at the hinder extremity, and are closely articulated 

 with one another. In the long-tailed groups the number of vertebrae is consider- 

 able ; but in the frogs and toads those of the back are reduced to seven or eight, 



SKELETON OF SALAMANDER. 



the hinder-end of the backbone terminating in a long style, extending between the 

 greatly produced extremities of the haunch-bones, or ilia, which articulate with the 

 lateral processes of the sacral vertebras. The transverse processes of all the 

 vertebrae are well-developed, and in some cases very long ; and they take the place 

 of ribs, which, at the most, are represented by some small rudiments. In conse- 

 quence of this absence of ribs, Amphibians are unable to breathe in the ordinary 

 way by alternate expansion and contraction of the cavity of the chest ; and 

 they, so to speak, swallow air, taking in a large gulp, and then closing the 

 mouth. In addition to the peculiarities connected with its condyles and the 

 basioccipital region, the skull is distinguished by its flattened, broad, and more or 

 less semicircular form ; the sockets for the eyes being generally large and ill-defined. 

 In front of the condyles the under surface of the middle of the skull is overlain by 

 a large parasphenoid bone, which is frequently dagger-shaped ; this bone being 

 generally but slightly, if at all, developed in the higher Vertebrates, although very 

 large in Fishes. The lower jaw, which articulates with the skull by the interven- 

 tion of a quadrate-bone, is composed of at least two pieces on each side and nay 



