74 AVES. 



the Swan, being the highest number. The atlas is depressed and 

 ring-shaped, arid generally articulates by its capsular surface with 

 the single condyle of the occipital bone, so that the head can be 

 freely rotated in a circle upon this joint, and directed completely 

 backward. In the Ostrich and Penguin a pair of smaller lateral 

 articulating surfaces are met with, which are directly confluent with 

 the central articulating cavity of the atlas, and receive two corres- 

 ponding divisions of the tubercle of the occiput, formed by the lateral 

 portions of that bone. The second cervical vertebra is deeper, and 

 has a processus dentatus ; its body is united to the atlas by a single 

 syriovial capsule ; an annular and a straight check ligament are met 

 with binding the processus dentatus to the atlas and tubercle of the 

 occipital bone. In Buceros the two superior cervical vertebrae are 

 blendid together and united into one. The rest of the cervical ver- 

 tebrae have oblique, transverse, and slightly-developed spinous pro- 

 cesses, namely, upon the middle part of the neck, and the most pos- 

 terior have also occasionally inferior spinous processes. The trans- 

 verse processes are very thick and strong, and have a double root, 

 so that they form a ring, and in the entire skeleton an interrupted 

 canal, within which the vertebral vessels and the cervical portion of 

 the sympathetic nerve are lodged. The bodies of these vertebrae 

 are very moveable upon each other, concave on their superior sur- 

 face, convex posteriorly, and are united by free capsular ligaments, 

 with only very thin intervening cartilages. The superior can be 

 moved usually more freely in the direction forward, the middle more 

 backward, and the inferior again forward, whence is produced the 

 peculiar sigmoid curve of the neck which is visible in the skele- 

 tons of most Birds. The spinal canal is of various form and width 

 in the several divisions of the cervical vertebrae, a condition which, 

 in long-necked Birds, has especial reference to the great degree 

 of mobility in the neck ; the roots of the spinous processes are also 

 united, for greater security during the numerous movements of the 

 vertebrae, by elastic ligaments, an arrangement which, along with 

 the preceding one, is plainly for the purpose of protecting the spinal 

 cord during the extensive inflections of the neck. The number of 

 dorsal vertebrae is in general less, and subject to fewer varieties ; 

 there are mostly found from 7 9, rarely 10, as in the Ostrich, Cas- 

 sowary, Goose, and still more rarely 11, as in the Swan and some 

 Ducks. They are but slightly moveable, and are often, especially 

 the hindermost, completely anchylosed together and to the sacrum. 

 This normal state of anchylosis, like that of the sacral vertebrae, was 



