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AXIAL SKELETON OF THE STRUTHIONID#. 
processes of which abut against the ilia just behind the acetabula (fig. 8, xxxu1, d & p, 
and fig. 9,p). After these vertebre there is a sort of gap, the nine anterior caudal 
vertebre either becoming entirely absorbed between the ilia or never being distinctly 
developed. Five imperfect, half-absorbed vertebre appear postaxiad of the ilia; and to 
them succeed six free and, in a sense, less incomplete vertebree, which terminate the 
series. Thus there are but twenty-three vertebre belonging to the first four categories, 
instead of twenty-seven as in Struthio. 
THE CERVICAL VERTEBRA. 
ATLAS AND AXIS OF RHEA (natural size). 
Fig. 3. Fig. 4. 

Shy 
Fig. 3. Preaxial view of atlas. Fig. 4. Lateral view of axis. 
ac, preaxial articular surface of centrum; d, diapophysis; #y, median hypapophysis ; /h, lateral hypapophysis ; az, prezygapo- 
physis; 4p, hyperapophysis; zs, neural spine; 0, odontoid process; pe, postaxial articular surface of centrum; pl, pleural 
lamella; pz, postzygapophysis of axis; z, postzygapophysis of atlas. 
The atlas, compared with that of Struthio, is relatively much more dorso-ventrally 
and less transversally extended. ‘The cup for the occipital condyle is nearly complete, 
having but a very small and narrow dorsal excavation. The lateral hypapophysial pro- 
cesses (fig. 3, /h) are more marked, and the median hypapophysis relatively smaller. The 
diapophyses (fig. 3, d), though distinct, are very much, even proportionally, smaller. No 
hyperapophyses are distinguishable; nor is there any costal bony spiculum. Even in 
the very immature specimen in the Museum of the College of Surgeons (No. 1361 F). 
the neural lamine are entirely ankylosed to the quasi-body, and show but.a trace of 
their own dorsal union. 
The azis (fig. 4) has a greater vertical extent than that of Struthio, while its antero- 
posterior excess over the atlas is much less. There is a pit below the odontoid process. 
The postaxial central surface is much more prolonged ventrad by the relatively much 
larger hypapophysis (fig. 4, iy), which also extends further towards the preaxial margin 
of the centrum. The neural spine (fig. 4, 2s) is relatively shorter (pre- and postaxially) 
and higher. The postzygapophyses are still more in excess of the prezygapophyses than 
in Struthio. A very large pneumatic foramen is placed above the parapophysial root 
BQ 
