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 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 ineptus. The length 

 of the cranial cavity (PL XXIII. 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 

 remarkable feature in the cranial structure of Bidus 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 Linornis^, the Owls, and a few large Cocka- 

 toos, e. g. Microglossmn 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 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 

 that cavity in Didus : the diploe gradually decreases in thickness as it approaches the 

 foramen magnum. The disposition of the osseous lameUse forming the ceUs or cavities 

 of the diploe 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 weU as in the superior or " roofing" wall of the cranial cavity. The 



' Proc, Zool. Soc. I. e. p. 6. 



2 Zool. Trans, vol. iv. pi. 24. fig. 4. 



' Odontography, pi. 146. fig. 1 ; Anat. of Vertebrates, vol. ii. p. 439. fig. 296. 



