430 AVES. 



rostrum at the point where they join one another. When the vomer is 

 small and pointed in front (or absent), and the maxillo-palatines do not 

 unite with one another and the vomer, the arrangement is termed schizo- 

 gnathous * (plovers, gulls, penguins, fowls, pigeons, etc.). The aegitho- 

 gnathous f arrangement (passerines, swifts) is similar to the schizogna- 

 thous excepting in the fact that the vomer is truncated in front. Lastly 

 when the vomer is small and the maxillo-palatines are large and spongy, 

 uniting with the maxillo-palatines or with each other across the middle 

 line ventral to the vomer the palate is described as desmognathous { 

 (anserine birds, birds of prey, parrots, etc.). 



In the vertebral column (Fig. 239) a long flexible cervical 

 region, a rigid thoracic, lumbar, and pelvic region, and a slightly 

 moveable, short, caudal region may be distinguished. 



The cervical and thoracic regions are not sharply distinct from 

 each other, since the cervical vertebrae, as in crocodiles, bear 

 double-headed ribs, the capitulum of which is fused with the 

 centrum and the tubercle with the transverse process, enclosing 

 between them the vertebrarterial canal. The last two cervical 

 ribs are free, but do not reach the sternum. The atlas is a ring- 

 like bone, and the axis possesses a peg-like odontoid process. 

 The articulating surfaces of the remainder of the cervical verte- 

 brae are saddle-shaped and without epiphyses (except in the 

 parrots). The neck is long and freely moveable and contains 

 nine to twenty- three (swan) vertebrae. The thoracic vertebrae 

 are fewer in number ; they all carry ribs which are united to the 

 sternum by a sternal portion (Stc), and to the vertebrae by a 

 capitulum which is attached to the centrum or lower part of the 

 arch and by a tuberculum to the transverse process of the neural 

 arch. The vertebral portions of the ribs carry backwardly 

 directed bony uncinate processes. The thoracic vertebrae are 

 sometimes slightly moveable upon one another, sometimes anky- 

 losed ; in the former case the articulating surfaces are saddle- 

 shaped, or as in the penguins, plovers, etc., are rounded, the 

 anterior surface being convex, the posterior concave. 



The rib-bearing thoracic vertebrae are followed by a tolerably 

 extensive region of the vertebral column in which the vertebrae 

 are fused with one another and with the long iliac bones of the 

 pelvic girdle. This is the compound sacrum and includes as 

 many as sixteen to twenty or more vertebrae. Of these one or 



* Alluding to the cleft between the maxillopalatine and vomer. 

 f &iyi$os, a finch. 

 J Setr/wi, a bond. 



