582 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 “touch-spots” in various parts of its skin. 
The axial skeleton.—The vertebral column consists of 
nine vertebra, 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 
vertebre, 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- 
4p., Transverse processes tiges in the centra of the verte- 
of sacral vertebra; /2, 
ilium; U., urostyle ; Fe., bree. 
ea 5 4seh., ischiae ~The skull consists — (a) of the 
persistent parts of the original car- 
tilaginous brain-box or chondrocranium, developed, as in 
the skate, from parachordals and trabecule, plus nasal 
and auditory capsules ; (4) 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, 
