100 OSTEOLOGY [Parr II. 
from the typical form; the inner ridge-like condyle is extended in the antero-posterior diameter, and rests 
in a corresponding groove on the articular element of the lower jaw ; while the flattened upper border of the 
thick and elevated outer wall of the latter, plays on a trochlear groove, extending externally along the 
posterior moiety of the base of the condyle. This ginglymoid joint permits the protrusion and retraction of 
the lower jaw, as in Parrots, for the purpose of unhusking fruit or seeds; the tympanic in the Didunculus, 
however, is readily distinguished from that in Parrots, by the double mastoid condyle. 
The lower jaw varies in strength in the same ratio as the upper; it is more or less curved in the 
different genera, and to the greatest extent in the slender-billed species, in which the beak is arched down- 
wards anteriorly. The dentary element is equal in length to the upper mandible; the posterior segment is 
much inflated in Geophaps; and in all has a triangular digastric facet, which m Diduneulus slopes very 
obliquely forwards and inwards, but in Geophaps has nearly the same shape as in the Dodo; the external 
angular plate is not developed in the lesser Pigeons. The form of the articular surface. necessarily varies 
with that of the coadapted aspect of the tympanic; the coronoid process is strongly developed in Diduneu- 
lus and Treron. The vacuity between the angular, surangular, and dentary elements, is present in Geophaps 
and Goura, asin the Dodo; but is obliterated in Didunculus and Treron. 'The separation of the opercular 
element in the Dodo, indicates the incomplete development of the individual, and it occurs in the same 
condition in the specimen of Geophaps figured; but in the huge inert Dodo, it may remain unanchylosed 
longer than in the more active and volatile forms. The symphysis is broad and depressed in Geophaps, but 
is more acute and ascending in Zreron, as in the Dodo. 
In Didunculus, the dentary element is very strong, and the core is armed, on each side, with two small 
crenations, supporting corresponding teeth-like processes of the gnathotheca, asin the Odontophorine among 
the Rasores: and the symphysis is truncate anteriorly as in Parrots, the horny sheath covering the apex 
being abraded, in the specimen examined, so as to expose the cutis. 
It is affirmed that this bird lives on bulbous roots ; it may also live on hard-coated fruits and seeds, as 
suggested by Mr. Gould; the form of the articular surfaces of the tympanic and of the lower jaw, indicates 
the habitual employment of the lower mandible for decorticating roots, or unhusking fruits and seeds, after 
they have been crushed between the powerful jaws, the lower assisting especially by its dental armature ; 
the depth of the impressions for the insertion of the masticatory muscles attests the strength of these actions. 
The preceding details, accompanying the unrivalled lithographs of the skull of the Dodo 
(Plates VIII, IX, [X%*), from the pencil of my esteemed friend Mr. Ford, (to whom I beg to 
return my sincere thanks,) will, I trust, be -sufficient to remove any doubt regarding the 
Columbine affinities of that extinct form; the additional evidence furnished by the foof remains 
to be examined. 
The evidence regarding the affinities of a newly discovered or extinct bird, deducible 
from the form and minute configuration of the metatarsus, is second in value only to that 
furnished by the skull. . 
‘The metatarsus, like the head, preserves, notwithstanding such variations as occur in the 
different genera and species of a common group, certain family characteristics, which are 
permanent; and which it is the province of the anatomist to eliminate, irrespective of 
absolute size. 
The importance of this enquiry to the ornithologist, has led to its investigation in a 
general manner by Kessler,' whose researches will, I trust, be published by the Ray Society. 
' Bulletin de la Société Impériale des Naturalistes de Moscou. Année 1841. 
