68 



ZOOLOGY. 



4. The Ribs and Sternum. The main part of each 

 rib is bony, but their ventral ends are cartilaginous. These, 

 in the case of the first seven pairs of ribs, articulate directly 

 with the sternum ; the next two pairs 

 (" false ribs ") join with the ribs in 

 front ; the remaining three (" floating 

 ribs ") end freely ventral wards. Occa- 

 sionally in the rabbit an extra pair of 

 floating ribs is found behind, making 

 thirteen in all : in such cases the corres- 

 ponding vertebra is counted as thoracic 

 instead of lumbar. The floating ribs 

 have no tuberculum. 



The sternum (fig. 29) is a metameric- 

 ally jointed bone. Its anterior joint 

 (manubrium) is large and projects for- 

 ward ; the next four are called sternebrce, 

 and the ribs articulate between these; 

 finally there is the xiphisternum, ending 

 in an expanded plate of cartilage. 

 So much for the thoracic vertebrae and related bones: 

 it must not be supposed that they do not differ among 

 themselves. On the contrary, the change from typical 

 thoracic to typical lumbar is quite a gradual one. We are 

 concerned here only with the main features, and the details 

 must be made out by the 

 student on the actual bones. 

 We now pass on to the other 

 regions of the column. Un- 

 less otherwise stated, centrum, 

 neural arch and spine, zyga- 

 pophyses, intervertebral pads 

 and epiphyses are everywhere 

 present. 



Fig. 29. STERNUM. 



Fig. 80. A CERVICAL VEHTEBBA. 

 Front view. 



5. Cervical Vertebrae (fig. 30). These are seven in 

 number. They seem, at first sight, to have no ribs. The 

 transverse processes differ from those of the thoracic series 

 in having paired longitudinal perforations, the vertebr ar- 

 terial canals, so called because, in life, the vertebral 



