The vertically expanded anterior part of the premaxillary (ib. fig. 1, 22) has a large pneumatic cavity communicating by a reticulate wall with the cells of a cancellous structure, larger than those of the cranial diploë. The maxillary branch of the premaxillary (ib. 22*) consists of a light open-work air-diploë, with a very thin outer case of bone. The short symphysis mandibulæ shows a small cavity, surrounded by more minutely cancellous structure and thicker compact walls, especially at the upper and hinder parts. Although some characters have been too much insisted on (_e.g._ the “superoccipital foramen”) as exemplifying the affinity of the Dodo, the more essential characters of the skull relate to its true Columbine character, while the deviations from that part of the skeleton of volant Doves are explicable in the adaptive developments needed for the wielding of long, powerful, massive mandibles, serving most probably to enable the bird to subsist on some proportion of animal diet, in addition to such vegetable food as it might gain from the ground. Such indiscriminate feeding doubtless rendered its flesh less palatable than that of the winged Pigeons of the Mauritius to the Dutch navigators of the sixteenth and seventeenth centuries. But the affinities of _Didus_ will be more fully and decisively brought out in the comparison of the, in this respect, more instructive and light-giving parts of the skeleton. § 3. _Comparison of the Skeleton._ The dorsal region of the vertebral column shows, in some birds, a confluence of certain vertebræ: I have observed four to be so welded together by both centrums and neural spines in _Phœnicopterus_, viz. the second to the fifth dorsal inclusive, leaving the sixth free, which articulates with the first costigerous sacral vertebra. In _Platalea_ three dorsals coalesce in advance of the antepenultimate free vertebra. In the smaller diurnal birds of prey five dorsal vertebræ are usually confluent, leaving one free vertebra for the lateral movements of the trunk between such dorsal “sacrum” and the pelvic one. In Vultures, Plovers, Bustards, Cranes, _Psophia_, _Cariama_, _Palamedea_, Auks, Penguins, and in all flightless land-birds save the Dodo, no such anchylosis takes place. The _Columbidæ_ are the species in which the dorsal vertebræ, homologous and the same in number with those of _Didus_, undergo the process of confluence into one mass of bone: they are the three which immediately precede the last (moveable) dorsal vertebra; and of these the two anterior develope, in _Goura_ and _Didunculus_, hypapophyses closely corresponding in shape and proportion with those in the Dodo.