ORIGIN AND CHARACTERISTICS 29 



relating to the osteology and digestive system 

 of birds. The skeleton of a bird may very 

 naturally be divided into three principal parts, 

 comprising the head, the trunk, and the limbs. 

 The vertebral column not only contains and 

 serves as a protection to the spinal cord, but 

 supports the head and limbs. It is composed 

 of a very variable number of units or vertebrae, 

 which are divided according to the position they 

 occupy into the following classes, viz., cervical 

 relating to the neck, dorsal to the back, sacral 

 or pelvic to the loins, and caudal to the tail. 

 The first cervical vertebra is termed the Atlas, 

 because it bears the head, and which is articu- 

 lated with it by a single occipital condyle. The 

 second, termed the Axis, because it is the pivot 

 on which the atlas and head turn, is consider- 

 ably longer and larger than the succeeding 

 cervical vertebrae, remarkable for their paired 

 or single ventral processes and vertical knobs, 

 when in the former condition assisting to pro- 

 tect certain blood-vessels, and when in the latter 

 serving for the attachment of the powerful 

 muscles which work the flexible neck. Suc- 

 ceeding these come the dorsal vertebrae, which 

 not only in many cases coalesce with each 

 other, but always do so with the sacral or pelvic 



