676 GEOLOGICAL SURVEY OF THE TERRITORIES. 
sessile, and in comparison with the bulk of the bone it is attached to, ar. 
insignificant tubercle, though unquestionably fulfilling all the impor- 
tant functions required of it. In less than six weeks the odontoidal lar- 
ceny is complete, and no trace remains to lead one to suspect how mat- 
ters stood at the earlier date. 
Immediately beneath and a little posterior to the primoidal and dis- 
tinct centrum of the atlas, there is another, and still larger, free ossific 
centre, uniform in outline, concave above, surrounding the primitive 
odontoid apophysis with its long axis lying transversely; behind, and 
in contact with it, are two more very minute and elliptical ones placed 
side by side. The first of these unite with the atlas and latterly form 
the bony ring for the occipital condyle to revolve in, and the surface for 
the odontoid to move upon, and a notched lip of bone that projects from 
it behind, that subsequently develops; the remaining two, behind the 
first ossicle mentioned, form the anterior part of the body of the axis 
that bears the articulating surface for the first vertebra. In the full- 
grown bird the postzygapophyses of the first vertebra projecting well 
to the rear look almost directly inward. They meet the prezygapoph- 
yses of the axis that face in a contrary direction and a little backwards. 
The articulating facet for the centrum of the axis is subelliptical, convex, 
of some size, and has in the segmented column the inferior and convex 
surface of the odontoid playing just above it, the superior and flat sur- 
face of the latter being confined by intervening and delicate ligament 
forming a part of the floor of the neural canal of this bone. In the axis 
of the adult the anterior part of the bone with the odontoid process, 
that was separately added, projects conspicuously forwards beyond the 
neural arch, and in birds of several months of age it can be distinctly 
discerned where the union was established between neurapophyses and 
centrum. 
In the mature vertebra the neural canal is nearly circular. In the 
center of the bone, above, a knob-like tubercle acts as the neural spine, 
which has mesially and behind a deep pitlet for the insertion of the in- 
terspinous ligament. Anapophysial tubercles are found above the post- . 
zygapophyses, which latter are of considerable size, concave, and faced 
downwards. The centrum of the axis is subcompressed from side to side 
and supports mesially, just anterior to the second vertebral articulation, 
the first hypapophysis of the series. The first two segments of the ver- 
tebral column are non-pneumatic. 
Vertebre throughout the chain in the young chick invariably show 
the line of union between the centra and neurapophyses, but it is lost 
as soon as the birds come to be two or three months old. At this age, 
however, still very interesting points of development are strikingly visi- 
ble in the third vertebra, which otherwise varies but slightly from the 
same bone in appearance as seen in the column of an old male, such as 
we have before us. 
The neural spine, more compressed than in the axis, is nearer the mid- 
dle of the vertebra, still deeply pitted for the interspinous ligament be- 
hind, and slightly so on its anterior margin. This characteristic becomes 
very faint among the long vertebra in the middle of the neck, to be more 
Strongly reproduced as we approach the dorsals, the posterior depres- 
sion always being by far the best defined. We find anapophysial tuber- 
cles still present in the third vertebra. These also exist throughout the 
cervical series, with more or less clearness; they form ridge-like lines 
upon the elongated segments of the mid-neck. The zygapophysial pro- 
cesses in general look upwards and inwards anteriorly, and vice versa be- 
hind—the fourth vertebra having in common with the one we are now 
