STUDIES OF 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 (Garrod), 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 tlie plan of articu- 

 lation seems to be truly " heteroccelous," 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 Trocjon 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, 



