5 62 



AMPHIBIA. 



lateral lines, but of this regularity the adult retains little 

 trace, though it has many nerve-endings and " touch spots " 

 in various parts of its skin. 



The axial skeleton. --The vertebral column consists of 

 nine vertebrae, and an unsegmented urostyle or coccyx. 



The first vertebra bears two facets for the two condyles of 

 the skull, and an odontoid process which lies between the 

 condyles. It has no transverse processes, and its arch is 



incompletely ossified. Each of the 

 next six has an anteriorly concave or 

 proccelous centrum, a neural arch 

 surrounding the spinal cord, a trans- 

 verse process from each side of the 

 base of the arch, an anterior and a 

 posterior pair of articular processes, 

 and a short neural spine. The eighth 

 vertebra has a biconcave or amphi- 

 ccelous centrum. The ninth is convex 

 in front, with two convex tubercles 

 behind, and bears large transverse 

 processes with which the hip-girdle 

 articulates. The urostyle, formed by 

 the fusion of several vertebrae, has 

 anteriorly a dorsal arch enclosing a 

 prolongation of the spinal cord ; but 

 both arch and nerve-cord soon dis- 



FIG. 272. Vertebral a ppe ar posteriorly. The notochord, 

 column and pelvic around which the vertebral column 



^ as developed, is finally represented 

 onl y b y the vestiges in the centra of 



the VCrtebnE. 



The sku11 consists - - (a) of the 

 persistent parts of the original car- 

 tilaginous brain-box or chondrocranium, developed, as in 

 the skate, from parachordals and trabeculae, plus nasal 

 and auditory capsules ; () of ossifications of parts of 

 the chondrocranium, cartilage bones ; (c) of membrane 

 or investing bones ; and (d] of associated visceral arches. 



Two ex-occipitals bounding the foramen magnum and forming the 

 condyles, two pro-otics or ossifications of the original auditory capsule, 

 and an unpaired sphenethmoid forming the front of the brain-case, are 



Fe. 



I sell. 



girdle of bull-frog. 



ilium; 17., urostyle; Fc. 



region: '"*" ^ 



