5 82 



AMPHIBIA. 



tadpole has sensory cells in distinct lateral lines, but of this 

 regularity the adult retains little trace, though it has many 

 nerve-endings and " toudi-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 sur- 

 rounding the spinal cord, a transverse 

 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 amphiccelous centrum. 

 The ninth is convex in front, with two 

 convex tubercles behind, and bears 

 large transverse processes with which 

 the hip-girdle articulates. The uro- 

 style, 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 disappear posteriorly. 

 FIG. 313. -Vertebral The notochord, around which the 

 column and pelvic vertebral column has developed, is 

 girdle of bull-frog. finally represented only by the ves- 

 /.A, Transverse processes tiges in the centra of the verte- 



pf sacral vertebra ; //., 

 ilium ; /., urostyle ; fe., DrSS. 



re^on ; / **" M "* c Tne sku11 consists (a) of the 

 persistent parts of the original car- 

 tilaginous brain-box or chondrocranium, developed, as in 

 the skate, from parachordals and trabeculse, plus nasal 

 and auditory capsules ; (b) of ossifications of parts of 

 the chondrocranium, cartilage bones ; (c) of membrane 

 or investing bones; and (d) of associated visceral arches 



Jsch. 



Two ex-occipitals bounding the foramen magnum and forming the 

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



