THE PIGEON. 185 



12. The capitular facet, a small articular surface on the 

 lateral surface of the centrum near its anterior end, and 

 giving articulation to the head of the rib ( 14). 



13. The hypapophysis, a vertical downwardly directed 

 process, proceeding from the middle vertical line of the 

 centrum. 



14. The ribs, small curved bones articulating, one on 

 each side, with the vertebra, and tapering from their proxi- 

 mal to their distal ends. The proximal end is divided into 

 two processes, one ventral, the head or capitulum, which 

 articulates with the capitular facet on the centrum, the other 

 dorsal, the tubercle, which articulates with the tubercular 

 facet of the transverse process. 



15. The uncinate process, a small flat plate of bone 

 given off from the posterior border of each rib, and directed 

 backwards and upwards. 



IV. In the remaining cervical vertebrae note : 



1 6. The gradual diminution from behind forwards of the 

 neural spines, transverse processes, and hypapophyses, and 

 the gradual elongation of the centra as far as about the third 

 or fourth vertebra. 



17. In the penultimate vertebra the rib is much smaller 

 than in the last, has no uncinate process, and its proximal 

 end is indistinctly divided into head or tubercle. 



1 8. The absence of free ribs in the remaining vertebras : 

 the apparent transverse process is, however, perforated by 

 an aperture, the vertebrarterial canal, for the passage of 

 the vertebral artery (Fig. 54, p. 232, vr), and the part of the 

 transverse process external to this aperture represents a 

 cervical rib, the head and tubercle of which have anky- 

 losed with the centrum and transverse process respectively. 



19. The characters of the second vertebra or axis : it is 

 considerably reduced in all dimensions : the anterior zyga- 



