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



The paroccifital processes pass gently forwards at their base into the zygomatic 

 process, in all save in the Tinamous and Apteryx, Rhea, and Dinornis. In Apteryx and 

 the Tinamous they are separated from the zygomatic process by a notch more or less 

 deep. In Dinornis they pass forward into the squamosal prominence, and there lose 

 themselves. In Rhea only, externally, they are continued upwards as a strong ridge to 

 join the posterior boundary of the temporal fossa, and, internally, sweep round towards 

 the middle line in the form of a thin, curved, laminated plate of bone to form the inner 

 boundary of the tympanic recess. 



The Roof of the Cranium (PI. XLII. figs. 1-4). — The roof of the cranium is 

 produced laterally, in front of the temporal fossa, into a pair of pendent post-orbital 

 processes, in all save Apteryx and the Crypturi. In the former, post-orbital processes 

 are entirely absent, and in the latter they are reduced to a mere prickle. The anterior 

 region of this roof, in all save Dinornis, Mpyornis, Apteryx, and Crypturi, is charac- 

 terized by a pair of very long outstanding and backwardly-directed spines, being the 

 elongated supra-orbital process of the lachrymal. In Struthio these are continued 

 backwards, by means of fused supra-orbital ossicles, to join the frontals ; thus enclosing a 

 space between the ossicles and the combined frontal and nasals (fig. 8). 



In Dinornis the lachrymal passes backwards insensibly into the frontal to form a 

 broad overhanging ledge to the orbit. In the Crypturi it projects conspicuously on 

 either side of the skull, but is without the backvvardly-projecting spines. In Apteryx 

 the lachrymal has become reduced to a mere vestige fused with the alinasal. 



In all save Apteryx and the Tinamous the frontal is produced laterally to form an 

 overhanging pent-house to the orbit. In Apteryx, the frontal passes downwards and 

 inwards in the form of a smooth convex infolding of the bone, leaving the orbit without 

 any sharply defined boundary ; and in the Tinamous this region is deeply hollowed out, 

 almost to the middle line, so that the interorbital region of the skull is very narrow. 

 Young skulls of Rhea and Dromceus resemble the Tinamous in this respect. 



There is a conspicuous cerebral dome in ^Epyornis and Dromceus ater. In profile, 

 in DromcBus ater, the skull slopes rapidly downwards and forwards in front of this dome; 

 in JEpyornis the gradient is much less marked. 



The inter-orbital region in Dromwus is very wide, in Rhea very narrow : thus, taken 

 in connection with the development of the supra-orbital processes of the lachrymals, 

 this forms a useful character for systematic purposes. 



In the Tinamidce the frontals bear shallow supra-orbital grooves. 



The Rase of the Skull (PL XLII. figs. 5-8). — Casuarius, Dromceus, Struthio, and the 

 Tinamidce all agree, more or less closely, in the form of the basitemporal platform. In 

 all, viewed below, it takes the form of a flattened, slightly tumid area, roughly penta- 

 gonal in shape, the base being caudad. Its postero-lateral angles are not produced into 

 mammillary processes, nor are there, save the Eustachian apertures, any sharply defined 

 boundaries forwards. Struthio and Dromceus somewhat closely resemble one another 



