xiii.] THE FROG. 213 



trum of the vertebra and not quite so wide as 

 the centrum in its antero-posterior diameter. 



a. The transverse process : a bony bar on each 

 side, arising from the arch and passing out- 

 wards and a little downwards. 



(3. The articular processes (zygapophyses); an an- 

 terior and posterior pair, springing from the 

 sides of the arch ; the anterior, having their 

 smooth articular surfaces directed upwards ; 

 the posterior with similar surfaces directed 

 downwards.. 



y. The short spinous process, springing from the 

 dorsal aspect of the arch and directed back- 

 wards. 



c. The neural canal enclosed between the arch and 

 the body. 



2. Examine the remaining vertebrae. 



a. The first vertebra (atlas): its body produced 

 forwards into a wedge-shaped process which lies 

 between the occipital condyles : its arch, some- 

 times incompletely ossified in the region "of the 

 spinous process, which is rudimentary; posterior 

 zygapophyses only present: the large concave 

 anterior facets, partly on the arch and partly on 

 the centrum, with which the skull articulates. 



b. The 2nd, 4th, $th, 6th and 7th vertebrae : closely 

 resembling the third, the chief differences being 

 found in the varying size and direction of the 

 transverse processes, all of which are smaller 

 than those of the third vertebra. 



