OCR Text |
Show 1899.] CRANIAL OSTEOLOGY OF THE PARROTS. 23 In Gacatua the auditory meatus is somewhat narrowed, much as in Psittacus, but to a varying degree in different species. In G. roseicapilla the ingrowth of the posterior wall is particularly well marked, and leaves a large circular notch above, where in Ps. erithacus we had a more pointed indentation; in G. gymnopus, on the other hand, the posterior margin is convex rather than concave : but though less marked in G. roseicapilla thau in the rest, it is very characteristic of the Cockatoos that the region between the descending occipital ridge and the posterior wall of the auditory meatus is extremely narrow. W e shall see that this, which perhaps deserves to be spoken of as the digastric area, differs greatly in extent in the different groups of Parrots. The suprameatal tubercle is distinct, and the triangular area below and in front of it is larger than in Psittacus. The region of the squamosal process overlapped by the fused posterior ramus of the prefrontal forms in G. roseicapilla a prominent projection extending backwards and downwards to overlap the shaft of the quadrate bone ; but in G. leadbeateri and G. ducorpsi this is not the case, the Fig. 14. Cacatua ducorpsi. posterior or inferior margin of the squamosal process running evenly forward and downward as in Psittacus. The paroccipital processes are large and point somewhat backwards; the basi-temporal ridges are prominent, but not continued directly on to the under surface of the paroccipital. The occipital condyle is considerably above the level of the base of the skull. The mandibular fontanelle is very small or obsolete. The paroccipital is but slightly excavated within ; the jugular foramen is small, except in C. ducorpsi, wThere it is considerably bigger. The two facets for the heads of the quadrate bone are distinctly separated by a ridge. The two heads of the quadrate are wide apart, and the inner is rather large, more than half as large as the outer. The pterygoid condyle is distinct, and in G. roseicapilla is more distinct than in the others from the main condyle or mandibular articulation. The shaft of the quadrate is distinctly stouter than in Psittacus, and the upper posterior portion of the body above the quadrato-jugal cup is not rounded off as in that genus, but conspicuously prominent. |