OSTEOLOGY OF THE DODO. 69 
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 Didwnculus 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 ineptus. The length 
of the cranial cavity (Pl. XXIII. fig. 1, vc) 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 
remarkable 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 aterrimum ; but it is fully paralleled only by the Elephant 
among air-breathing vertebrates, as may be seen by comparing the section Pl. XXIII. 
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 diploé 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 diploé above the cerebral cavity equals the vertical diameter of 
that cavity in Didus: the diploé gradually decreases in thickness as it approaches the 
foramen magnum. The disposition of the osseous lamelle forming the cells or cavities 
of the diploé is very different in the Elephant and Dodo: they extend for the most part 
vertically between the outer and inner tables of the skull in the proboscidian mammal, 
leaving long and narrow interspaces ; in the heavy ground-bird they form a congeries 
of small subequal and subspherical air-cells, and this structure obtains in the basal and 
lateral walls as well as in the superior or “ roofing” wall of the cranial cavity. The 
' Proc, Zool, Soc. 7. ¢. p. 6. 
2 Zool. Trans. vol. iv. pl. 24. fig. 4. 
3 Odontography, pl. 146. fig. 1; Anat. of Vertebrates, vol. ii. p. 489. fig. 296. 
