STUDIES OE THE MACROCniRES. 
325 
The hypapophysial processes of the fifth, sixth, seventh, and 
eighth cervical vertebrae part mesially in order to form a canal 
for the protection of the left carotid artery, the only one present 
in these birds (Gfarrod), as it passes to the head. 
Upon the last few cervicals, and upon the first two or three 
dorsals, very well-developed hypapophyses are to be found, which 
may become tricornuted towards the latter end of the segments 
specified ( T puella). 
Diapophyses of the dorsal vertebrae are notoriously broad, with 
their outer extremities rounded, being considerably wider even 
here than the bodies of the ribs that articulate beneath them ( T . 
mexicanus) . 
Below, the centra of these dorsal vertebrae are deep and much 
compressed laterally ; their median, longitudinal, inferior lines 
being almost cultrate in character. 
The dorsal neural spines are all nearly of the same height, but, 
on the whole, rather low in point of altitude. Their superior 
rims are thickened, and interlock at their anterior and posterior 
ends. These five dorsal vertebrae, although freely articulated, are 
very closely moulded upon each other, and consequently the mo- 
bility of this division of the column is somewhat limited. 
Facets for the vertebral ribs are here, as usual, found for each 
pair just within and posterior to the anterior margins of the 
centra of the respective vertebrae at their lateral aspects. 
Thus far in the column of these Trogons the plan of articu- 
lation seems to be truly “ heterocoelous,” i. e. the ends of the 
centra present saddle-shaped facets, which in turn lock with 
a counter-placed one on the opposed face of the vertebra next 
behind. 
Of the Sternum. — Leaving the vertebral column for the moment, 
we will turn our attention to this bone. There is a good deal in 
the sternum of Trogon to remind us of the same part of the 
skeleton in Geococcyx ; of which we may at once satisfy ourselves 
by comparing the figures of the bone as it is found in these two 
forms and shown in my plates. Figures of the sternum of Trogon 
mexicanus illustrate this memoir (PI. XIX. figs. 12, 13), while 
corresponding views of it for Geococcyx are to be found in the 
plates of my contribution upon the osteology of G. californianus 
in the ‘Journal of Anatomy and Physiology ’ for 1886. 
Among the Trogons the sternum is short, and, when taken in 
comparison with the size of these birds, rather expansive behind, 
