38 MR. ST. GEORGE MIVART ON THE 
THE DORSAL VERTEBR2. 
These vertebre, the seventeenth, eighteenth, nineteenth, and twentieth, differ from the 
dorsal vertebre of all other Struthionide in the great and the equal development of 
their neural spines, as also in the great relative axial extent of their diapophysial pro- 
cesses. In them the hypapophysis gradually diminishes postaxially in size, becoming 
quite rudimental in the nineteenth vertebra. The twentieth vertebra has the ventral 
surface of its centrum axially grooved. The last two dorsal vertebra may be slightly 
ankylosed together ventrally. 
THE DORSO-LUMBAR VERTEBRZ. 
These vertebra (the twentg-first to the twenty-fourth inclusive) are more in number 
than in any other of the Struthionide. ‘They all have equally high neural spines ; and” 
these are equal in height to those of the dorsal vertebre ; also, like the latter, they are 
much extended axially. The diapophyses are similarly extended axially ; and the centra 
are similarly antero-posteriorly grooved. The twenty-first vertebra may be slightly 
ankylosed ventrally to the twentieth. 
THE LUMBAR AND LUMBO-SACRAL VERTEBR/. 
The vertebre from the twenty-fifth to the thirty-second inclusive compose the lumbar 
region. ‘They are, of course, all ankylosed into one mass, which on its ventral surface 
may be flat, or transversely concave, so as to present an axially directed groove. ‘Trans- 
verse processes are present in the four or five most preaxial vertebra, but not more 
postaxially (7. ¢. not in the lumbo-sacral vertebra), none others being visible when the 
pelvis is viewed ventrally. Thus there comes to be a conspicuous narrow and elongated 
fossa on each side between the ilium and acetabulum and the vertebral column. 
PELVIS OF APTERYX (j natural size). 
Fig. 41. 













Ventral view. 
