26 ANATOMY OF THE RABBIT 



one group and thus serve as criteria for determining to which 

 group any single vertebra of a disarticulated skeleton belongs. 

 The distinguishing character of the cervical vertebrae 

 (Fig. 5) is the presence of the vertebrarterial (transverse) 

 foramen in the transverse processes of all seven of these 

 vertebrae; that for the thoracic vertebrae (Fig. 6) is the pres- 

 ence of costal demifacets on the centra, for articulation with 

 the head (capitulum) of the ribs, and tubercular facets on the 

 transverse processes, for articulation with the tubercle of the 

 ribs. The costal demifacets are represented by a whole facet 

 entirely on the cranial ends of the vertebrae of the last three, 

 or four, centra. Definite tubercular facets are absent on the 

 transverse processes of these vertebrae. The distinguishing 

 characters of the lumbar vertebrae (Fig. 7) are absence of 

 costal and tubercular facets. The transverse processes are 

 long and extend craniolaterad, and the centra are very heavy. 

 The three sacral vertebrae (Fig. 7) are fused together and the 

 intervertebral foramina are divided into a small dorsal and a 

 large ventral foramen. The first two vertebrae contribute to 

 the formation of the auricular processes, by means of which 

 the sacrum articulates with the innominate bones. The 

 caudal vertebrae progressively degenerate; the neural canal 

 is lost first, then the processes, so that the last eight vertebrae 

 are little more than cylindrical centra. 



C. RIBS AND STERNUM 



The rabbit commonly has twelve pairs of ribs, but, as in man, 

 a thirteenth pair is sometimes found. The ribs are curved, 

 flattened bones which articulate with the vertebrae dorsally 

 and the first seven with the sternum ventrally by means of 

 costal cartilages. The last five are ''floating" ribs, that is, 

 they are not directly attached to the sternum. 



A typical rib (Fig. 9) has a head (capitulum) with which it 

 articulates with the costal demifacets of two contiguous thoracic 

 vertebrae, a tubercle, with which it articulates with the trans- 



