38 
to the provision of unwonted strength of heak in the Dodo. The maxillary branches 
of the premaxillary have completely coalesced with the maxillaries, as these have with 
the palatines ; and the halves of the upper mandible here swell out laterally and more 
so vertically, the maxillaries rising to combine with the outer divisions of the nasals, and 
sending back a short process from their lower and lateral part to join the malar. The 
inner surface of the maxillary process (PI. XI. fig. 1, 22 *) is smooth and slightly convex 
vertically ; both upper and lower borders are obtuse and thick. 
The palatines arch outward from their posterior attachments, are broad and smooth 
mesially ; the margin here is angular, with a slightly produced obtuse apex, divided by 
a channel on the under surface of the palatine from the outer convex border ; the upper 
and outer ridge extends forward to the maxillary ; the inner one subsides before 
reaching that bone. “ The palatines form the posterior boundaries of the naso- 
palatine aperture, and approximate each other at both ends, but more closely posteriorly, 
yet here without meeting ; whilst in Didunculus they coalesce before receiving the 
abutment of the pterygoids. 
“ The tympanic bone is subquadrate, with the four angles produced, and the upper 
and hinder are bifurcate, forming the double condyle for the mastoid articulation” \ 
There is a larger pneumatic foramen, communicating with the tympanic cavity, between 
the articulating cavities for these condyles. 
The brain is singularly small in the present species of Didus : and if it be viewed as 
an index of intelligence of the bird, the latter may well be termed inej)tus. The length 
of the cranial cavity (PI. XI. fig. 1, c) is 1 inch 8 lines, its extreme breadth 1 inch 
6 lines, its greatest height 1 inch (and this is at the cerebellar fossa). The most re- 
markable feature in the cranial structure of Didus is the disproportionate size of the 
brain-case to the important part of the neural axis it contained and protected : some 
approximation to this condition is made by Dinornis^, the Owls, and a few large Cocka- 
toos, e. g. Microglossum aterrimmn ; but it is fully paralleled only by the Elephant 
among air-breathing vertebrates, as may be seen by comparing the section PI. XI. fig. 1 
with the figures of a similar section quoted below ^ * 
Not only was the brain of very small proportional size in the present large extinct 
bird, but the division of the cranial cavity appropriate to the cerebrum proper is less in 
proportion to that for the cerebellum and optic lobes, at least in vertical and longitu- 
dinal diameters, than in any other known bird. 
In the Elephant the thickness of the pneumatic diploe between the fore part of the 
cerebral cavity and that of the outer cranial wall equals the longitudinal diameter of the 
cavity containing the cerebral hemispheres : in Didus it exceeds that diameter. The thick- 
ness of the pneumatic diploe above the cerebral cavity equals the vertical diameter of 
' Proe, Zool. Soo. 1. c. p. 6. 
® Zool. Trans, vol. iv. pi. 24. fig. 4. 
’ Odontography, pi. 146. fig. 1 ; Anat. of Vertebrates, vol. ii. p. 439. fig. 296. 
