166 
PEOFESSOE OWEN ON THE VEETEBEAX 
The neurapophyses, resting on each side of the upper half of the centrum of the atlas, 
converge and articulate above with two small tubercles (figs. 31 and 32, z) on the fore- 
part of the neural arch of the axis, almost meeting but not uniting above the nem-al 
canal (fig. 28, n). 
The body of the axis (figs. 29, c^) is eight times larger than that of the atlas: it 
expands posteriorly, and terminates by a transversely elliptical ball (d) at the upper part 
of that end, and in a pair of thick short obtuse diverging apophyses (j)') at the lower 
part. There is a rudimental hypapophysial ridge (fig. 33, /ly) from the middle and 
toward the fore-part of the under surface of the centrum. There is no trace of a hyp- 
apophysis, free or anchylosed, below the body of the atlas. 
The centrum of the axis-vertebra is confiuent with the neural arch : at the middle 
of the side, apparently crossing the hne of junction, is a large subcircular aperture 
(fig. 29, o), which leads directly into the widely cancellous structure of the bone below 
the neural canaL This vacuity, as in the other cervicals, answers to the ‘foramen 
pneumaticum ’ in the vertebrae of birds, and doubtless admitted a production from the 
air-cells extending along the neck of the Pterodactyle into the cancelli of the osseous 
tissue. The neural arch (n;T) rests upon the three anterior fourths of the centrum ; it 
expands as it passes backward ; and there, also, as it rises, until it sends off from each 
posterior angle the zygapophysis (z'), which has a tubercle above, and a fiat articular 
surface below, looking downward and a little outward and backward. The small 
tubercles at the fore-part of the neural arch (fig. 31, z), to which the neurapophyses 
of the atlas are ligamentously connected, may be the stunted homologues of anterior 
zygapophyses. The neural spine begins by a low ridge between those tubercles, increas- 
ing rapidly in thickness behind ; but it has not been preserved in its full height in any 
specimen. 
In the small atlas and axis (figs. 32 — 34) the line of sutm’e between the bodies of 
these two vertebrae is distinct. In a somewhat larger specimen, the centrum of the 
atlas was separable by a smart blow, and showed the true anterior surface of that ot the 
axis (fig. 31); it is very slightly concave with a submedian prominence. A vertical sec- 
tion of the anchylosed atlas and axis is shown in fig. 30 : the neui’al canal (7i) expands 
at its posterior outlet : the large cancelli of the centrum are filled by the matrix. 
On comparing the atlas and axis of the Pterodactyle mth that of the Pil'd, the Ostrich 
for example, the atlas in the bird is represented by the neurapophyses which have 
coalesced below with a hypapophysis, forming an irregular ring of bone. The centrum 
has coalesced with that of the axis forming a small prominence convex anteriorly, and 
filling up the vacuity at the upper part of the cup excavated in the fore-part of the hyp- 
apophysis : the neurapophyses are broad in the bird, and overlap the anterior zygapo- 
physes of the axis : they meet above the neural canal, but retain the separating fissure 
there in the Ostrich. The centrum of the axis is broader before than behind. A short 
process, like a connate pleurapophysis from' the fore-part of the centrum, miites ulth a 
diapophysis from the neural arch to form an arterial canal. The pneumatic foramen is 
