| OCR Text |
Show 270 MR. W. T. PYCRAFT ON THE [Mar. 17, to the vertical face of the posterior division of the neognathine mesethmoid, that is, exactly in front of the antorbital plate of the adult. To make the fissure complete, the incision would have to be continued downwards so as to completely bisect the plate, whilst the rostrum would have to terminate at the free edge of the posterior segment of the plate. In the adult skulls the incipient fissure remains, placing the light and left olfactory chambers, in the dried skull, in communication. The formation of a complete cranio-facial fissure is correlated with, and perhaps consequent 011, the reduction in the length of the parasphenoidal rostrum, which in all the Palseognathae is of great length. I11 a skull of a half-grown Casuarius salvadorii it is, however, relatively much shorter than in an adult C. australis, and much overhung by the mesethmoid. Whether this peculiarity obtains also in the adult of this species I am unable to say. The olfactory cavities do not extend backwards in the Cuculi or Musophagi, so as to lie 011 either side of the mesethmoid, as in the Tubinares for example; the antorbital plate arising in the plane of the cranio-facial fissure. The quadrate does not differ materially from that of the adult. The articulare is still distinct. b. The 2fembrane-bones. The parietal is oblong in shape, its anterior and posterior borders sinuously curved, its mesial border straight, and its external lateral border being slightly convex. It is bounded in front by the parietal, behind by the supraoccipital, and laterally by the squamosal. The frontal has its hinder border sinuously curved, and throughout the greater part of its length applied to the parietal. Its postero-external is closely applied to, and ultimately fuses with, the supero-anterior angle of the squamosal and the postorbital process of the alisphenoid. In the supraorbital region it turns downwards and inwards to form a broad overlapping plate articulating with the alisphenoid. From the mid-orbital region onward it becomes band-shaped, ultimately being produced Into an outwardly directed and blunt angle underlying the nasal. The squamosal is roughly quadrate in form, and has the superior anterior angle produced into a linguiform process which overlaps the parietal and alisphenoid. Its antero-ventral angle is produced into a small squamosal prominence, the under surface of which affords the articular surface for the squamosal head of the quadrate. The postero-ventral angle is obliquely truncated, and forms the anterior segment of the rim of the tympanic cavity. The supero-posterior angle is produced into a slight point which is wedded in between the parietal and lateral occipital. The hinder border of the squamosal serves to cover in the recessus tympanicus superior, which is formed by the absorption of the diploe of the lateral occipital. |
