SHUFELDT. ] _ OSTEOLOGY OF THE TETRAONID. 677 
describing an interzygapophysial bar, lending to these two segments 
that broad and solid appearance well known to ornithotomists, not pos- 
sessed by any other of the cervicals. The neural canal in the third ver- 
tebra is nearly circular, which is also its form in the adult, becoming 
only moderately compressed from above downwards in the last three or 
four cervicals. Regarding the third vertebra from below, we observe 
that the articulating surface of the centrum for the axis to be quite con- 
cave and turned a little downwards. The processes that fall beneath the 
prezygapophyses form what would be a canal with its lateral margins; 
this groove, however, in the “bird of the year” is converted into the ver- 
tebral canal by an independent ossicle being placed over it on either 
side, and, being below the rest, it causes a broad shailow concavity to 
appear mesially and anteriorly. 
These small bones have at the very outstart stumpy apophyses project- 
ing backwards, which are the parapophyses of the vertebra—the pro- 
jections they meet from above being the pleurapophyses, the groove they 
form mesially being the broad termination of the carotid canal. 
The fourth vertebra has the same general appearance of the third, that 
we have just been describing; it is a little longer, however, and in both 
large pneumatic foramina are found laterally and beneath’ the diapoph- 
yses. ‘These apertures are found in the vertebral canal in the remain- 
der of the cervicals. Again, in both, the bodies are rather compressed 
from side to side, and itis not until the bird has arrived at maturity that 
the hypapophyses are well seen in these two segments. 
Now, taking up the cervicals from the fifth vertebra, we find certain 
characteristics holding good throughout the series, with certain gradual 
modifications. In the adult the neural spine in the fifth is prominent and 
placed anteriorly ; it slowly subsides to the tenth, where it is more tuber- 
ous, nearer the middle of the bone, and bears. evidence of having a 
posterior projection overhanging the depression for the interspinous, 
ligament. This is the type to include the thirteenth, the projection being 
more and more prominent and slightly cleft behind ; in the fourteenth 
and fifteenth it suddenly assumes the broad quadrate spine of the dor- 
sal'type. Returning to the fifth vertebra, we note another change in 
the lengthening of the postzygapophyses; the acme of this modification 
is seen to be in the sixth and seventh vertebra. From these they gradu- 
ally shorten again, while the anterior ones spread out with the dia- 
pophyses to assume the form of the consolidated ones in mid-dorsal col- 
umn. This arrangement allows lozenge-shaped apertures to exist be- 
tween the segments above, and subelliptical ones laterally, that become 
smaller and more circular above as the postzygapophyses shorten, and 
quite large laterally as they approach the point opposite where the bra- 
chial plexus is thrown off from the myelon. 
In the adult Cock of the Plains we detect beneath, in the fifth ver- 
tebra, well anteriorly, a strongly-developed quadrate hypapophysis. 
This process entirely disappears in the sixth, for in this segment the 
centrum of the bone, anteriorly on either side, just where the parapo- 
physes meet the body mesiad, a tubercle commences to make its appear- 
ance, the apices slightly inclined towards each other. From the sixth to 
the tenth inclusive these apophyses become longer, approach each other 
below, but never meet so long as they have the “carotid canal,” which 
they form between them. In the eleventh they seem to have met through- 
out their extent to form a hypapophysis on the exact site they occupy 
in the tenth, the tenth vertebra being the last cervical where there is 
any evidence of the carotid canal; hence from this method of formation 
Professor Owen is made to say (Comp. Anat. and Phys. of Vertebrates, 
