AXIAL SKELETON OF THE OSTRICH. 387 
dorso-lumbar vertebra, there being three such with ribs, the first of which is connected 
by a styliform bone with the side of the sternal rib of the last true dorsal vertebra. 
The next eight vertebre (twenty-eighth to thirty-fifth) do not support long rib-like 
processes and are constantly anchylosed into one mass in adults; they may be called 
lumbar vertebre. 
Next follow three vertebra with long distally expanded rib-like processes abutting 
against the ilia. It will be at least convenient to call these sacral vertebre. 
At the distal end of the sacral mass we have in the adult eight vertebree (thirty-ninth 
to forty-sixth), which may be termed sacro-caudal vertebra. 
Finally there are ten postsacral vertebrae normally free in the adult, except the last 
two; these ten are the true caudal vertebra (fig. 1*). The number of these vertebree 
may sometimes, however, be reduced to eight’. 
There are thus normally fifty-six vertebre from the atlas to the coccyx inclusively. In 
some skeletons, however, there may be one or two vertebrae short or a vertebra in ex- 
cess ; and when such divergences exist, the differential characters of all the various ver- 
tebree are correspondingly modified ; and this should be borne in mind when the descrip- 
tion here given is compared with such skeletons. 
THE PRESACRAL VERTEBR~. 
Tue CrervicaAL VERTEBRA. 
Tue Atias.—The atlas of the Ostrich presents an extreme contrast to the same bone 
in all mammals, even the lowest, in that it is so small a bone, being little more than an 
osseous ring, ventrally thickened with three short postaxial projections, and not being 
more than a quarter the bulk of the axis. 
Nevertheless, though this vertebra as a whole is relatively so small compared with the 
atlas of mammals, yet that part of it which is median and ventral (é. ¢. that hypapo- 
physial ossification which holds the place of a “ centrum”) is relatively much larger 
than in any mammal. This might perhaps be anticipated from the articulation of the 
vertebral column with the skull being median in birds, through a single condyle, instead 
of lateral as in mammals through a pair of condyles. 
The atlas of the Ostrich consists of this guast body and two neural lamin, which 
meet together dorsally, but do not develop a neural spine. 
The whole vertebra in the adult consists of one bone, no trace remaining of the 
primitive separation between the neural laminz and the median ventral portion. 
This latter (the guasi-body) apart from its junctions with the neural arch, may be 
said to have four surfaces—one ventral, one dorsal (or neural), one preaxial, and one 
postaxial ; and these four surfaces are divided by four corresponding margins. 
The preaxial surface of the centrum, which articulates with the occipital condyle, 
’ As in the mounted specimen, No. 1362, in the Museum of the College of Surgeons. 
Dues 
