vi.] GENERAL CHARACTERS. 65 



vertebra behind ; but sometimes chiefly or entirely either 

 to one or the other. They are usually articulated movably 

 to prominences (hypapophyses) on the lower surface of the 

 body of the vertebra, but occasionally become ankylosed to 

 it. They ossify from two centres, one on each side, which | 

 usually coalesce in the median line below, though not unfre- 

 quently, especially at the beginning and end of the series, 

 where they are less developed, the two lateral portions remain 

 >rmanently separate. They serve to give a larger surface of 



FlG. 29. — Anterior surface of fourth caudal vertebra of Porpoise {Phcaena com- 

 munis), i. s spinous process; m metapophysis ; / transverse process ; h chevron 

 bone. 



attachment for the inferior muscles of the tail, and also to 

 protect the caudal vessels, which run within the canal formed 

 by the series of these bony arches. They are always best 

 developed near the anterior extremity of the tail, and are 

 never found under the posterior rudimentary vertebrae. 



In Man the caudal vertebrae are quite rudimentary ; 

 usually 4 in number, all ankylosed together, and constituting 



F 



