68 ORGANS OF SUPPORT, 



XX. Amphibia. The amphibious or batrachian animals 

 commence their career as fishes, with one auricle and one 

 ventricle, and breathing by means of gills which in many 

 are retained through life, but in their adult state they ac- 

 quire a pulmonic respiration, arid a pulmonic auricle of 

 the heart, and this early aquatic life and subsequent meta- 

 morphosis affect the whole condition of the skeleton, and 

 the forms of the several bones. The skeletons of the am- 

 phibia come nearest to those of fishes in the imperfect 

 ossification, and the thin, diaphanous, elastic character 

 of the bones, in the loose condition of the bones of the 

 face, and in the imperfect development of the ribs. The 

 perennibranchiate amphibia, and the tadpoles of the 

 caducibranchiate species, present the softest and the most 

 detached condition of the bones, and the most fish-like form 

 of the whole skeleton. Their vertebral column is prolonged 

 backwards to a great extent, as an organ of motion ; their 

 arms and legs are wanting, or are very imperfectly developed, 

 and their os hyoides, like that of a fish, supports a variable 

 number of branchial arches, as seen in the annexed figure 

 of the skeleton of the proteus anguinus (Fig. 33.) The ver- 



FIG. 33. 



tebrse here have the bodies terminated before and behind by 

 concave surfaces, as in fishes, and all the processes of these 

 vertebrae are short, to allow of extensive motion, especially in 

 a lateral direction. There is no sacrum, and the pelvic (&,) and 

 scapular (#,) arches are as free as in fishes. A few small de- 

 tached points of bone at the ends of the transverse processes 

 of some of the anterior dorsal vertebrae are the only ribs here 

 developed ; and in this, as in many other characters, the pro- 

 teus and the siren resemble the sharks. The parietal (e,) and 

 the frontal bones are long and separate, the tympanic bone is 

 long and moveable. The wide inferior jaws, the long in- 

 termaxillaries, and the loose upper jaw-bones are provided 

 with sharp, recurved, conical teeth. The body (,) and 



