316 PROF. ST. GEOEGE MIVAET ON THE 



These vertebrae may be subdivided as follows — '16 cervical, 1 cervico-dorsal', 5 dorsal, 

 4 lumbar, 3 lumbo-sacraP, 3 sacral, 4 sacro-caudaP, and 6 caudal, besides the pygostyle. 



The whole axial skeleton is exceedingly pneumatic, each vertebra being very light, 

 and having a swollen appearance with smooth surfaces and ridges, and processes but 

 little developed. Hyperapophyses and metapophyses are small ; and only three or four 

 vertebrae have conspicuous hypapophyses. 



Besides the cervical vertebrae, the two following ones are also generally movable. 



The rest of the dorsal vertebrae and the lumbar vertebrae have their bodies ankylosed 

 together, and somewhat compressed laterally, but not remarkably so. 



The Cervical Vertebrae. 



The cervical vertebrae unite so as to form angles with one another, open ventrad till the 

 seventh's junction with the eighth, which forms an angle open dorsad, as does that of the 

 eighth with the ninth, and so postaxiad till they unite without forming an angle at all. 



The ATLAS, compared with that of Struthio, is narrower transversely in proportion to 

 its antero-posterior extent (Plate LV. figs. 1 & 2). 



Viewed preaxially, the dorsum of the neural arch is more visible, because its pre- 

 axial part is more inclined ventrad. The odontoid notch is relatively deeper, and has 

 the minute secondary notch on the middle of its dorsal margin more marked. The 

 dorsal ends of the preaxial articular surface are produced more preaxiad, and rise 

 dorsad slightly above the level of the outward process, which they embrace. There is 

 no diapophysis. 



Postaxially, the ventral surface of the neural arch is more visible for the reason above 

 given ; the odontoid notch is deeper ; and the articular surface of centrum is more 

 curved, but scarcely at all produced preaxially on the neural surface of the centrum. 



Ventrally. there are either no catapophyses (or lateral hypapophysial processes), or 

 they are quite minute, while the median hypapophysis is less produced postaxiad 

 relatively than in Struthio. 



Viewed laterally, the preaxial margin of the pedicel of the neural arch is very 

 slightly concave, while its postaxial margin is almost as concave as in Struthio. There 

 are no hyperapophyses ; and the zygapophyses are very small and inconspicuous. 



The preaxial margin of the centrum is more concave than in Struthio, on account of the 

 greater production preaxiad of the dorsal parts of the preaxial central articular surface. 



Seen dorsaJhj, the postaxial margin of the neural arch is less concave than in Struthio, 

 on account of the less postaxiad production of the zygapophyses. 



The pedicels of the neural arch are very slender. 



The AXIS is inclined more dorsad postaxially upon the atlas than in Struthio ; it is 



' With movable ribs wbicb do not reach the sternum, and -n-ith no lateral vertebral canal. 



' The pelvic vertebras without parapophyses. 



' Postsacral vertebrae forming part of pelvic mass. Sometimes there are but three of these. 



