348 MESSES. A. AND E. NEWTON ON THE OSTEOLOGY OE THE SOLITAIRE. 
and still more from that of Didunculus. In the sudden vertical narrowing of the den- 
tary in front of its junction 'with the surangular (Plate XXII. fig. 160) Pezophaps 
shows a greater approach to some of the more normal Columbce , Treron for example. 
While in Didunculus the lower mandible sweeps on with a continuous downward curve, 
and in Didus it exhibits but a slight projecting angle at its splenial region (in both cases 
preserving nearly the same vertical height throughout), in Pezophaps (the upper edge of 
the whole mandible being apparently much straighter than in Didus) the angular and 
surangular slope steeply down to meet the dentary, which immediately afterwards rises 
as steeply, thereby forming on its lower edge a salient angle altogether wanting in Di- 
dunculus and not very considerable in Didus. From this the dentary rapidly tapers till 
it descends to form the gonys, which is fully as much developed proportionately as in 
Didus , while the angle formed by the two rami at their symphysis is somewhat more 
acute, and thus, with the less massive proportions of the upper mandible already de- 
scribed, the whole bill of Pezophaps must have been very much more slender and less 
powerful than the formidable, not to say monstrous weapon of Didus. The various 
foramina for the passage of the different nerves or vessels are situated much as in Didus. 
This is especially noticeable in the case of the large dental canal, which opens externally 
nearer the upper than the lower edge, while in Didunculus it occupies a position nearly 
midway. 
The proximal portion of the lower mandible (Plate XXII. figs. 159, 161) offers further 
differential characters between Didus and Pezophaps. Notwithstanding the small size 
of the entire head in the latter, the angular and articular bones are fully as large as in 
the former, though neither the internal pyramidal process nor the external semilunar 
plate are so largely developed. The basal facet therefore assumes a very different form. 
Instead of presenting as in Didus the shape of a nearly isosceles triangle, the equal angles 
of which are subtended by the sides forming the internal process, it is in Pezophaps more 
equilateral ; its extreme width only slightly exceeds its height, and its nearly vertical 
surface is less concave. The walls of the articular surface also are much thicker abso- 
lutely, and of course still more so comparatively, in Pezophaps than in Didus, and that 
which supports the concave reniform tract on its outer surface thrust out as to form a 
much more considerable projection in place of the elongated tubercle in Didus. As if 
further to add to the solidity of this part of the jaw, the tract for the insertion of the 
external pterygoid muscle is perceptibly less deeply concave. 
Of the quadrate or “tympanic” (Plate XXII. figs. 163-168), the collection includes 
nineteen specimens. We have not had any opportunity of comparing this bone in 
Pezophaps with the same in Didus, and the latter has not been figured separately, but 
only represented in situ, and consequently with some of its parts foreshortened and 
concealed. To judge, however, from the figures, the bone in the two birds is of much 
the same general form, though in Didus the angle formed by the mastoid articular 
segment and the orbital process seems to he more filled up than in Pezophaps, thereby 
making this process more slender, while in Pezophaps the mandibular condyle appears to 
