HIGH SCHOOL ZOOLOGY. 93 



resjnratovy organ, and in the disappearance of tliose nerve- 

 endings which are only adapted for a watery medium. Accu- 

 mulations of cutaneous glands are best seen in the toad, behind 

 the ear (parotoid) and elsewhere ; they secrete an acrid fluid 

 which must be regai-ded in the light of a defensive provision. 

 Horny changes in the epidermis or bony plates in the skin, 

 which are common in the Reptiles, are rare in the Anura. 



18. As in the Urodela, the skull of the Anura rests upon 

 the vertebral column by two condyles ; it pi'esents in other 

 respects important differences, e.g. the girdle-like ossification of 

 the cai'tilage in the orbital region, and the great reduction of 

 the hyoidean apparatus brought about by the disappearance 

 of the gills. Again, the vertebral column is very much 

 shorter, and its end together with the pelvis have been much 

 modified, in siach a way as to offer a solid basis of resistance to 

 the legs in leaping. The shoulder-girdle is very different from 

 that in the Menobi'anch, chiefly in the median meeting of the 

 precoracoids and coracoids, and the presence of an episternum in 

 front, and of a sternum behind that symphysis. In the skeleton 

 of the limbs, likewise, we find much change, chiefly in the fusion 

 of the bones of the fore-arm and lower leg, in the great length 

 of the proximal bones of the tarsus, and in the incompleteness 

 of its distal row. 



19. In accordance with the gait of the Anura, the muscula- 

 ture of the hind-limb is extraordinarily developed, and the 

 muscles of the trunk are no longer the chief locomotive organs. 

 Apart from the fact that in the frog the brain is somewhat 

 shorter, its olfactory lobes fused, and the optic lobes larger, there 

 is little difference between the central nervous system in the 

 Urodela and Anura. The ear, however, presents a well-marked 

 difference, for there is a tympanic membrane, bounding on 

 the outside a tympanic cavity, which communicates with the 

 mouth by an Eustachian tube. This tube is comparable to the 



