41 
(ib. 22 *) consists of a light open-work air-diploe, with a very thin outer case of bone. 
The short symphysis mandibulse shows a small cavity, surrounded by more minutely can- 
cellous 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 athnity 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 com- 
parison 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 vertebrae : I have observed four to be so welded together by both centrums and 
neural spines in Phoenicopterus, 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 vertebrae 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, Cariania, Palamedea, Auks, Penguins, 
and in all flightless land-birds save the Dodo, no such anchylosis takes place. The Colum- 
hidw are the species in. which the dorsal vertebrae, homologous and the same in number 
with those of Ihdus, 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 Pidunculus, hypapophyses closely corresponding 
in shape and proportion with those in the Dodo. 
The chief difference which Pidus offers in the present region of the vertebral column 
from that of Columbidw is in the greater number of the vertebrae or segments which 
are typically completed by bony haemapophyses articulating with pleurapophyses and 
directly with their mass of coalesced and expanded haemal spines constituting the ster- 
num. Of these typical thoracic segments there were five in Pidus (PI. III.) ; Pidvm- 
culus (ib.) shows four ; Goura three. In both existing genera these segments are suc- 
ceeded by a single one, anchylosed to the fore part of the sacrum, but with the pleur- 
apophysis long and moveable, with its haemapophysis terminating in a point before 
reaching the sternum, and extensively connected with the antecedent haemapophysis or 
sternal rib : in both genera two dorsal vertebrae in advance of the typically complete one 
G 
