THE VEETEBRiE IN BIRDS. 277 



birds theii" form frequently becomes much modified in the 

 adult ; and tliey develope prolongations, wbicb extend down- 

 wards and inwards, and protect the carotid artery or 

 arteries. 



The neural arches have well developed pre- and post- 

 zygapophyses. The ribs of one or two of the posterior 

 cervical vertebrse become elongated and freely moveable in 

 the CarmatcB, as in the Batitce. 



The first dorsal vertebra is defined as such, by the union 

 of its ribs with the sternum by means of a sternal rib ; 

 which not only, as in the Crocodilia, becomes articulated 

 with the vertebral rib, but is converted into complete bone, 

 and is connected by a true articulation with the margin of 

 the sternum. 



The number of the dorsal vertebrae (reckoning under that 

 head all the vertebraj, after the first dorsal, which possess 

 distinct ribs, whether they be fixed or free) varies. The 

 centra of the dorsal vertebrae either possess cylindroidal 

 articular faces, like those of the neck, as is usually the 

 case ; or, more or fewer of them may have these faces 

 spheroidal, as in the Penguins. In this case, the convex 

 face is anterior, the concave, j)Osterior. They may, or may 

 not, develope inferior median processes. They usually pos- 

 sess well marked spinous processes. Sometimes they are* 

 sKghtly moveable upon one another; sometimes they be- 

 come ankylosed together into a solid mass. 



It is characteristic of the dorsal vertebrae of Birds that 

 the posterior, no less than the anteiior, vertebrae present a 

 facet, or small process, on the body, or the lower part of the 

 arch, of the vertebra for the capitulum of the rib, while 

 the upper j)art of the neural arch gives off a more elongated 

 transverse process for the tuberculum. Thus the trans- 

 verse processes of all the dorsal vertebrae of a bird resemble 

 those of the two anterior dorsals of a crocodile, and no 

 part of the vertebral column of a bird presents transverse 

 processes with a step for head of the rib, like those of the 

 great majority of the vertebrae of Crocodilia, Dvnosauria, 

 Dicynodontia, and Pterosauria. 



