PHYLOGENY OF THE PALZOGNATHE AND NEOGNATH.E. 197 
The pro-6tic completely shuts out the squamosal from the interior of the skull in all 
but Apteryx. In this type a large, roughly triangular plate appears immediately above 
the pro-étic and wedged in between the parietal and alisphenoid. 
The floccular fossa is deep, and oblong in all but Apterya, the long axis running 
vertical to that of the skull. In Apteryx it is represented by a small but deep and 
perfectly circular pit. 
Externally, the pro-6tic appears only within the tympanic cavity and affords two more 
or less distinctly separated articular surfaces for the quadrate: the one lying slightly 
above and in front of the other. Distad of the superior glenoid surface lies a similar 
articular surface furnished by the alisphenoid; caudad of the inferior lies a second 
facet furnished by the exoccipital. ‘These appear to be most distinctly traceable in 
Casuarius. Externally, articular surface for the quadrate is completed by the squamosal 
Thus there are two pro-dtic, one exoccipital, one alisphenoid, and one squamosal 
articular facet for articulation of the quadrate. 
The opisthotic is seen as a small oblong nodule of bone wedged in between the pro- 
Stic and the exoccipital, and bounded above by the inferior end of the epiotic. It is 
not visible externally. 
The foramen for the vagus lies at. its ventral extremity and between it and the exoccipital. 
The dasisphenoid has in every case fused completely with the underlying basi-temporal 
plate, and is therefore traceable only from the superior aspect of the skull. It is 
moderately thick in section, the body of the bone being thickened by a mass of diploé. 
It is bounded behind by the basi-occipital, laterally by the pro-6tic and alisphenoid. 
Anteriorly, in Rhea, it is produced forward into a thin vertical plate of bone, to join the 
cartilaginous presphenoid; in the other forms this vertical plate is much shorter. It 
serves to form the inner half of the circumference of the foramen for the orbito-nasal 
nerve (Y.), the outer portion being contributed by the alisphenoid. Out of its 
anterior region is scooped the pituitary fossa. The abducent foramen pierces it on 
either side near its postero-lateral angle. It forms the floor of the anterior region of 
the metencephalic fossa. 
In Apteryx it is almost quadrangular. In Casuarius and Dromeus, and in Rhea, it is 
expanded laterally to form a pair of wings, and is narrower behind than in front. 
The alisphenoid is bounded by the parietal and squamosal behind, the orbital plate of 
the frontal above, and the combined basisphenoid and alisphenoid as rings of the 
parasphenoid. 
In Dromeus, Casuarius, and Rhea it bears a share in the formation of the post-orbital 
process. 
The alisphenoid lodges the greater part of the mesencephalic fossa, and contributes 
a share towards the formation of the anterior wall of the cerebral fossa. 
The orbitosphenoid is represented only by cartilage and is much reduced in size. 
‘The presphenoid is represented by a thin vertical plate of cartilage resting upon the 
vo. xvy.—Ppart y. No. 12.— December, 1900. YAS 
