OSTEOLOGY 117 



tinamous I have not seen in the adult skeleton any free 

 intercentra ; nor in the Grues, excepting Chitnga. 



Further details on this matter will be found in the paper 

 cited below. 1 



Though free intercentra are by no means universal 

 among recent birds, hypophyses of the last caudals are 

 almost so. That these latter are derived from intercentra, 

 and are, therefore, not comparable to the hypapophyses of the 

 cervicals and dorsals, is clear from such cases where the gra- 

 dual transition between free intercentra and fixed hypapophy- 

 ses is shown. In reptiles the intercentra are in the tail region 

 constantly in the form of chevron bones, which are V-shaped, 

 articulating with the vertebral column by the free ends of 

 the V. This form of the hypophyses of the caudal region is 

 not so common as a simply bifid condition, but does oc- 

 casionally occur. I have seen it, for example, in Tubinares, 

 Accipitres, and Cuculi. 



The first vertebra of the cervical series is called the 

 atlas (see fig. 66) ; it is a ring on bone, of which the greater 

 part of the ' centrum ' is formed by the projecting odontoid 

 process (see fig. 67), the rest being formed by a pair of 

 intercentra. In the hornbills the atlas is fused with the 

 following axis vertebra. 2 Generally the atlas has not what 

 the succeeding vertebrae have, a vertebrarterial canal, but 

 this is sometimes present (see under ' Kibs,' p. 119). The 

 odontoid process sometimes notches the lower part of the 

 atlas, and sometimes perforates it. These two conditions 

 are illustrated by figs. 66 and 68. It sometimes happens that 

 the neural arch of the atlas is incomplete, e.g. CJuuti/u, 

 Colius, Pandion. As a rule it is perfect. 



In the cervical vertebrae the chief facts which appear to 

 be of systematic importance are the relations to each other 

 of the paired processes, to which MIVART has applied the 

 name of catapophyses. These are sometimes inconspicu- 

 ous processes of the transverse processes on the under 

 side. Very often the last one or two pairs of them closely 



1 BEDDAED, 'Note upon Intercentra,' &c., P. Z. S. lsi7, p. 4>'<~>. 

 - In a specimen of Chunga I have found the same fusion. 



