212 



CLASS AVES. 



ture Ratitae the cervicals have ribs articulating with an upper and a 

 lower process, as in the Crocodilia ; and in the adult (fig. 1104) 

 these ribs anchylose to the vertebrae, and thus resemble perforated 

 transverse processes, in which the canal (/) serves for the protection 

 of the vertebral artery. 1 In adult Carinatse these lateral arches, as 

 they may be termed, become further modified, and develop pro- 

 longations for the protection of other parts of the vasculo-neural 

 system. The dorsal vertebrae are liable to variation in number; 

 their centra usually resemble those of the cervical region, but in 

 the Penguins the articular surfaces of some may be spheroidal an- 



Fig. 1104. — (a) Anterior and (b) posterior views of a cervical vertebra of Hesperornis regalis ; 

 from the Cretaceous of North America, s, Neural spine ; z, Prezygapophysis ; z', Postzygapo- 

 physis ; d, Transverse process, or diapophysis ; j>, Rib-facet, or parapophysis ; nc, Neural canal ; 

 /, Costal canal. (After Marsh.) 



teriorly. 2 They usually have well-marked neural, and may or may 

 not have inferior median spines ; and they are in some instances 

 anchylosed together, but in others are susceptible of a limited 

 amount of motion. Throughout the whole dorsal series there is a 

 well-developed transverse process from the arch for the tuberculum 

 of the rib ; while the centrum has a lateral facet for the capitulum. 

 The method of costal articulation resembles, therefore, that obtaining 

 in the first two dorsal vertebrae of the Crocodilia. These features 

 are characteristic of all Birds. The dorsal vertebrae are succeeded 

 posteriorly by a number of anchylosed vertebrae forming the sacrum. 

 According, however, to the researches of Dr Gadow, only two or 

 three of these vertebrae are truly sacral ; those in front belonging to 

 the lumbar, and those behind to the caudal region. Of the proper 

 sacrals the two hindmost correspond to those of the Crocodilia, and 

 the second of these to the single sacral of the Amphibia. The ver- 

 tebrae articulating with the ilia do not develop ribs, but articulate 



1 This arrangement of the ribs is precisely similar to that occurring in certain 

 Dinosaurs, as is shown in fig. 1071 (p. 1 170). 



2 Certain Water and Wading Birds as well as Parrots, and the remarkable 

 Stealomis have opisthocoelous dorsal vertebrae. The Parrots also have epiphyses 

 to these vertebrae. 



