198 Mil. W. P. PYCKAPT ON THE MOKPHOLOGT AND 



parasphenoidal rostrum and wedged in between mesethmoid in front and the anterior, 

 laterally compressed vertical plate of the basisphenoid just described. It extends 

 upward and backward to the orbital plate of the frontal. From this region it sends 

 outwards and backwards a pair of cartilaginous wings, which represent the orbito- 

 sphenoids. 



The mesethmoid, in all but Apteryx, in common with the presphenoid region, forms 

 a conspicuous interorhital septum. In the nestling Droiiuens, Casuaritis, Rhea, and 

 ■? Ostrich, and in the adult Tinamou, this is pierced by a large interorhital fenestra. 

 This fenestra appears to be excavated partly out of the large, backwardly directed 

 plate which unites with the orbital plate of the frontal, and partly (caudad) out of the 

 anterior border of the presphenoid. In the nestling, the antero-ventral border is more 

 or less linguiform, and terminates at the level of the anterior border of the lachrymal. 

 From this, there runs forward a narrow, triangular, cartilaginous septum nasi. In the 

 adult Casuarius, Drommis, Binornithidce , and Tinamous, ossification extends forwards 

 almost to the end of the rostrum, and terminates in a vertical truncate border, beyond 

 which there is a small cartilaginous septum nasi. In Rhea and Struthio the ossification 

 extends quite to the free end of the rostrum, /. e. relatively further forwards, and 

 terminates in a sharp point instead of a vertical truncated border. In these, the 

 cartilaginous septum nasi is wanting or greatly reduced. 



The dorsal border of the mesethmoid, in Drovneiis, Casuarius, and Di)iornithid(e, is 

 of considerable thickness and very slightly convex ; it forms a complete floor to the 

 olfactory fossa, extending outwards on either side to the orbital plate of the frontal 

 (PI. XLIV. fig. 4). In this particular, as will be seen later, it differs conspicuously 

 from Apteryx, wherein this region forms a thin median partition between two extensive 

 cavities. At the anterior end of the olfactory fossa, both in Uromceus and Casuarius, 

 it sends upwards, and then backwards, a strong median pillar deeply grooved on either 

 side for the passage of the olfactory nerves. This corresponds to the tegmen cranii 

 described in Apteryx by T. J. Parker, and referred by Kitchen Parker to the tegmen 

 craiiii of the lower vertebrates. Thus the crista galli, in these two forms, is furnished 

 entirely by this tegmen ci-anii, the " tegminal process " of Jeffery Parker. 



At the apex of this tegminal process, as has been well described by Parker, tlie 

 mesethmoid reaches the outer surface of the skull; here it throws out lateral horizontal 

 ecto-ethmoidal plates — the aliethmoids, as Jeft'ery Parker proposed to call them. In 

 Drommis the upper surface of these plates forms a lozenge-shaped area, bounded by 

 the frontals behind, the nasals laterally, and the nasal process of the premaxilla in 

 front. The free edges of these right and left aliethmoidal plates in the nestlings turn 

 downwards and inwards (PL XLIV. fig. 4), and in the adult become further extended 

 and intricately folded to form the lower region of the aliethmoid and the antorbital 

 plates. In the nestling DrorncBus it should have been remarked that the median vertical 

 portion of thb mesethmoid is pierced by a large vacuity, the cranio-facial fissure. 



