THE FROG 35 
strate all the bones, both in the articulated and disarticulated 
skeletons. 
The skeleton of the frog may be conveniently divided into: 
(a) the axial skeleton, including the skull and the vertebral 
column, and (b) the appendicular skeleton, including the limbs 
and the limb girdles which attach them to the body. What evi- 
dence of metameric segmentation do you find in the skeleton of 
the frog? 
A. The Axial Skeleton—1. The vertebral column consists of 
nine vertebre and a posterior unsegmented portion, the coccyx 
or so-called urostyle. 
(a) Select a typical vertebra, for example the fourth, for 
careful study. Observe that it forms a bony ring, enclosing a 
central neural canal which during life is occupied by the spinal 
cord. The floor of the canal is formed by the centrum of the 
vertebra, which in the complete vertebral column is joined to the 
centra of adjacent vertebre by means of pads of fibro-cartilage. 
The neural arch comprises the lateral and dorsal portions of the 
ring and forms the sides and roof of the neural canal. Project- 
ing dorsally and posteriorly from the top of the neural arch is the 
spinous process or neural spine. The transverse processes are a 
pair of large projections extending horizontally outwards from 
the sides of the neural arch. The two pairs of articular 
processes or zygapophyses, situated respectively on the anterior 
and posterior borders of the neural arches, articulate with cor- 
responding processes of adjacent vertebre ; the anterior articular 
processes or prezygapophyses face upward and slightly inward, 
while the posterior articular processes or postzygapophyses face 
downward and slightly outward. Draw a posterior view of a 
vertebra (X 4). 
When all its:parts are in place the vertebral column forms a 
more or less complete tube for the protection of the spinal cord, 
but at the sides of this tube, between the successive vertebre, are 
openings, the intervertebral foramina, through which nerves pass 
out from the spinal cord. 
(b) Special vertebre. The first vertebra or atlas articulates 
with the skull; how? This vertebra has no transverse process; 
why? In the complete skeleton, observe the large gap on the 
