1899.] 



CEANIAL OSTEOLOGY Or THE PARROTS. 



23 



In Cacatua the auditory meatus is somewhat narrowed, much as 

 in Psittacus, but to a varyiug degree in different species. In 

 C. 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 0. gijmnopas, 

 on the other hand, the posterior margin is convex rather than 

 concave : but though less marked in C. roseicapilla than in the 

 rest, it is very characteristic ol: the Cockatoos that the region 

 between the descending occipital ridge and the posterior wall of 

 the auditory meatus is extremely narrow. We shall see that this, 

 which perhaps deserves to be spoken of as the digastric area, 

 differs greatly in extent in the ditferent 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 ot" the squa- 

 mosal process overlapped by the fused posterior ramus of the 

 prefrontal forms in 0. roseicapilla a prominent projection extend- 

 ing backwards and downwards to overlap the shaft of the quadrate 

 bone ; but in C. leadheateri and C. ducorpsi this is not the case, the 



Fie. 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 backvs'ards; the basi- 

 temporal ridges are prominent, but not continued directly on to 

 the under surface of the paroccipital. The oci-ipital condyle is 

 considerably above the level of the base of the skull. The man- 

 dibular fontauelle is very small or obsolete. The paroccipital is 

 but slightly excavated within ; the jugular foramen is small, except 

 in C. ducorpsi, where 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 C. roseicapilla is more distinct 

 than in the others from the main condyle or mandibular articu- 

 lation. 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 con- 

 spicuously prominent. 



