vi.j GENERAL CHARACTERS. 71 



certain bones, formed more or less in the form of an in- 

 verted arch (Fig. 29), called chevron bones (French, Os en V ; 

 German Untere Bogen ; h&mapophyses, Owen). These are 

 always situated nearly opposite to an intervertebral space, 

 and are generally articulated both to the vertebra in front and 

 the vertebra behind ; but sometimes chiefly or entirely either 

 to one or the other. They are usually articulated movably 

 to prominences (Jiypapophyses) on the lower surface of the 

 body of the vertebra, but occasionally become ankylosed to 



FIG. 29. Anterior surface of fourth caudal vertebra of Porpoise (Pkoc&na com- 

 initnis), i. ^ spinous process ; 111 metapophysis ; t transverse process ; h chevron 

 bone. 



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

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

 frequently, especially at the beginning and end of the series^ 

 where they are less developed, the two lateral portions remain 

 permanently separate. They serve to give a larger surface of 

 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 



