388 MR. ST. GEORGE MIVART ON THE 
presents a crescentic, transversely extended concavity, as it were a cup, with a consider- 
able median dorsal portion cut away for the reception of the odontoid process of the axis 
vertebra (fig. 2, ac). 
ATLAS VERTEBRA (natural size). 
Fig. 3. 
Aspects. 
Fig. 2, preaxial; 3, postaxial ; 4, lateral ; 5, dorsal; 6, ventral; 7, preaxial of immature bone. 
ac, Preasial articular surface of centrum ; ac’, portion of such surface formed by neural lamina; d, diapophysis or tubercular 
process ; kp, hyperapophysis ; hy, hypapophysis ; pe, postaxial articular surface of centrum; pe’ lateral prolongation of the same 
surface ; v, canal for vertebral artery (the spiculum of bone which encloses this is seen to be wanting on one side); x, a rounded 
tubercle representing a lateral hypapophysial process ; 2, postzygapophysis. 
The dorsal margin of this preaxial surface forms thus a strongly concave line; and its 
ventral margin is bounded by a longer line of generally similar curvature (the horns of 
the crescentic articular surface being as broad as its middle); but the median portion of 
the ventral margin may occasionally be slightly produced (as in the specimen 1362 B), 
so as to cause that margin to present a rounded prominence. 
The postaaial surface, which is applied to the centrum of the axis ventrad of the odon- 
toid process, presents a crescentic transversely extended articular surface (fig. 3, pc, p¢). 
This surface is gently convex dorso-ventrally, but straight and flat transversely. Its 
upper margin is strongly concave, and is produced preaxially on each side, the postaxial 
articular surface of the quasi-body thus extending on each side somewhat on to the dorsal 
(neural) surface of the same part, and there articulating with the sides of the ventral 
surface of the root of the odontoid process. 
‘The ventral margin of the postaxial surface of the atlas is more or less convex, with 
its median portion drawn out into a postaxially projecting hypapophysial process (figs. 3, 
A, & 6, hy). 
The neural surface of the quasi-body is gently concave transversely, with a marked 
pit (fig. 5) in its midst, no doubt for a ligament proceeding dorsad to the pit at the root 
of the odontoid process on its ventral aspect. 
