182 MR. W. P. PYCRAFT ON THE MORPHOLOGY AND 



deep shelf. This is less marked in Rhea. In Dinornis and Crypturi it is but feebly 

 developed. 



The cerebral fossa? in Dinornithidce do not taper forwards to finally pass into the 

 infundibuliform olfactory fossae, but, on the contrary, are of great size and width in this 

 region, reducing the olfactory fossae to the dimensions of shallow pits. 



The median bony falx, continued forwards from the tentorial ridge to the crista 

 galli, is extremely well developed in Casuarius and Dromceus, less so in Rhea, 

 and only feebly in Struthio and Dinornis and Tinamous. There is no trace of it 

 in Apteryx. 



In Casuarius and Dromceus the fossse bear distinct and deep impressions for the 

 temporal and frontal lobes, a low ridge indicating an indistinct Sylvian fissure. 



The olfactory fossce in all, save Dinornis and Apteryx, are paired, more or less 

 tubular, infundibuliform chambers, separated one from another by a crista galli. 

 Anteriorly they are closed by a more or less perforated plate for the passage of the 

 olfactory nerves. 



In Dinornis the olfactory fossa? take the form of shallow pits lying at the anterior 

 end of the large cerebral fossa. The cribriform plate is large. 



In Apteryx these fossa? are of great size, and pass insensibly backwards into the 

 cerebral fossa?. They are not, in the dried skull, shut off anteriorly from the turbinals 

 by a cribriform plate as in other Ratitoe, but continued forwards directly into the 

 olfactory chamber. 



The Premaxilla. 



The premaxilla in all the Palceognathce is peculiar, in that the nasal process is 

 median, and not paired as in all other birds (PI. XLII. figs. 1-3). In all save 

 Struthio there are well-developed palatine proceses. 



In Casuarius the beak is more or less laterally compressed. The body — that 

 portion of the premaxilla from which the nasal, maxillary, and palatine processes are 

 given off — is short, and more or less deeply grooved on either side, so that the distal 

 end of the nasal process seems to be continued forwards into a strongly marked ridge. 

 The maxillary processes extend backwards as a pair of slender splints to the level of 

 the lachrymal on either side. The palatine processes are a pair of short narrow 

 lamina? extending backwards to a point corresponding with a vertical line passing 

 upwards behind the top of the free end of the median nasal process. They enclose 

 anteriorly a small chink-like palatine notch. In C. australis there is a small pre- 

 narial septum, corresponding to that described by Parker in Dinornis, as the " strong 

 ascending keel, formed posteriorly of paired plates, but solid in front and gradually 

 diminishing in height towards the top of the beak." This keel is derived from the 

 dorsal surface of the palatine processes. 



The nasal process is rod-like, its free end passes backwards into a tunnel-shape 

 in the inflated, mesethmoid mass forming the characteristic casque of these birds. 



