594 MR. ST. GEORGE MIVART ON THE 
The neural spine is excavated by a fossa (for a ligament) on its postaxial surface (fig. 
10, f); but preaxially it dips gradually to the preaxial border of the neural arch, with- 
out either excavation or process of any kind. 
The neural arch encloses a space which is smaller than that enclosed by the neural 
arch of the atlas; and the transverse diameter of this space is especially diminished, 
the arch thus appearing less low relatively. 
When viewed in its dorsal aspect (fig. 11), the neural arch is seen to expand 
greatly postaxiad, its transverse diameter between the postzygapophyses being double 
that between the prezypapophyses. Its preaxial margin is concave, with a median 
preaxial projection; its postaxial margin is generally more or less slightly concave. 
No foramina are developed other than those already noted. 
The immature condition of the axis vertebra (as seen in the specimen 1397 a of the 
College-of-Surgeons Museum) shows that the neural lamin become perfectly anchy- 
losed together and to the centrum at a time when the neural lamin of the atlas remain 
altogether distinct, as also the odontoid process (or rather “ bone ”) itself. 
The odontoid bone forms a very large part of the so-called centrum of the axis, as 
well as the whole of the odontoid process itself (fig. 14, ac). All the articular surfaces 
of the axis for the quasi-body of the atlas are formed by this odontoid bone, except 
the little surfaces at the sides of the ventral surface of the root of the apparent odon- 
toid process of the adult. These are seen to be formed by the preaxial ventral ends 
of the neural lamine themselves (fig. 13, ac’). 
At this early stage, the lateral perforations of the vertebra (one just postaxial to the 
diapophysis, and one at the side of the centrum and placed more ventrally) are relatively 
larger and much more conspicuous. 
Tue THIRD VERTEBRA. 
The third vertebra exeeds the axis in size very much less indeed than the axis exceeds 
the atlas. 
Its most striking difference in appearance from the axis depends on the absence of 
the odontoid process and the larger development of the prezygapophyses, which give 
the bone a quadrate appearance when viewed dorsally, instead of that preaxial tapering 
which marks the axis (fig. 15). 
The vertebra consists of the same parts as the axis, except the odontoid process; and 
these are similarly fused into one solid and complex bone. 
As to the centrum, its preavial surface, which joins the postaxial surface of the 
centrum of the axis, presents a transversely extended articular surface, very concave 
from side to side and convex dorso-ventrally; both the dorsal and ventral margins of 
this surface are strongly concave, while its lateral margins are slightly convex. The 
whole articular surface looks more yentrad than preaxiad (figs. 16, 17, ac). 
The postaxial surface does not differ from its preaxial surface in shape nearly so 
