260 MEMOIRS OF THE CARNEGIE MUSEUM. 
margin of the transverse process unite to form a deep lateral horizontal sinus 
between them. 
The odontoid process is conical. Its transverse greatly exceeds its vertical 
diameter. It is relatively longer in the male than in the female. The faces for 
articulation with the atlas are concave horizontally and convex vertically, and 
unite to form continuous surfaces with the anterior articulating faces of the centrum, 
which have the same curvatures. Its anterior extremity shows a combination in 
Fic. 28. 1, anterior view of axis of M. elatus (No. 1604), X 4; 2, posterior view of axis of M. elatus (No. 
1604) X 4; 3, posterior view of axis of M. petersoni (No. 1703A), <3. 
structure of the ‘‘peg”’ and the “spout.’’ The neural canal on the upper side of 
the odontoid divides into two grooves, semicircular in section on either side of the 
peg-like extremity of the bone, which points upward between these two grooves. 
A deep notch for the second pair of spinal nerves occurs in front at the point 
of union of the pedicle with the centrum. 
The spinous process is strongly developed antero-posteriorly, as well as verti- 
cally. It overhangs the odontoid in front. In the case of the specimens referred 
by me to the female sex the antero-posterior dimensions of the spine are markedly 
less in proportion to the rest of the bone than in specimens attributed to the male 
sex. At the back of the superior margin the spine is thickened in all cases, but 
much more in the two specimens, Nos. 1604 and 1713, which are regarded as having 
belonged to males. In the former of these the hinder margin of the spine swells 
out into more or less hemispherical masses on either side, and in specimen No. 
1604 these lateral thickened masses are separated from each other above on the 
median line by a sulcus extending backward and gradually becoming deeper 
posteriorly. 
