THE RABBIT 425 



lower part, into which fits a peg, the dens or odontoid 

 process, projecting forward from the centrum of the second 

 vertebra. This peg represents the centrum of the atlas 

 removed from it and fused with the vertebra behind. The 

 transverse processes of the atlas are very broad, and the front 

 side of the vertebra has two very large articular surfaces for 

 the occipital condyles. The second vertebra is known as 

 the axis or epistropheus. It has a long, crest-like neural spine 

 and bears the odontoid process. The remaining cervical 

 vertebrae are short and broad, with low neural spines, except 

 that of the seventh. The thoracic region contains twelve or 

 thirteen vertebras, which are characterised by bearing mov- 

 ably articulated ribs. The neural spines are long, the trans- 

 verse processes short and stout, and each, in the first nine 

 vertebras, provided on the under side with a facet or " costal 

 pit " for articulation with the tubercle of a rib, presently to be 

 described. The front end of the centrum (in the first nine the 

 hinder end also) bears on each side a facet for the head of the 

 rib. The hinder vertebras of this set gradually become more 

 like those of the lumbar region. These are usually seven in 

 number. They are characterised by their large size and the 

 great development of their processes, the prezygapophysis 

 being borne upon the inner side of a large metapophysis and 

 the hinder intervertebral notch being overhung by a small 

 anapophysis. In the first two the centrum bears a median 

 ventral hypapophysis. The lumbar vertebras have no ribs. 

 There is usually only one sacral vertebra, but sometimes two 

 are found. These vertebras are large and bear at the sides 

 a pair of wing-like expansions, which support the hip girdle 

 and are probably ribs fused with the vertebra. A certain 

 number of the succeeding vertebras are fused with the true 

 sacral vertebra, the whole mass being known as the sacrum. 

 The caudal region contains about eighteen vertebras, of which 

 the first three or four are fused with the sacral. They 

 grow smaller from before backwards, losing their processes 

 and becoming degenerate. 



The ribs are present as independent elements only in the 



thoracic region. They are curved, bony rods, 

 Breastbone, articulated with the vertebrae. Those of the 



first nine pairs are connected at their lower ends 

 with the breastbone by bars of calcified cartilage known 

 28 



