10 PROF, d'arct w. THOMPSON ON THE [Jan. 17, 



shown), the auditory region, and the quadrate bone, there are very 

 numerous conditions to be distinguished, which appear likely to 

 help in the search for natural affinities. 



The following pages contain an account of the skull in different 

 genera, with particular reference to three of the above-mentioned 

 characters. The descriptions and figures are taken partly from 

 specimens in my own collection, which is considerable, and partly 

 from skulls belonging to the Eoyal College of Surgeons and 

 to this Society, for the opportunity of studying which in" Dundee 

 I am very greatly obliged to Mr. C. Stewart and to Mr. Beddard. 

 The genera are described for the most part in the order of Count 

 Salvadori's British Museum Catalogue, and I attempt to show in 

 the sequel certain cases where osteology suggests a different 

 arrangement. 



The accompanying diagrams of the skull and quadrate of Psit- 

 tacus erithacus (figs. 1 & 2) show the characters to which attention 

 will be chiefly drawn in the descriptions, 



Ke. 1. 



Psittacus erithactos. 



pr.o., preorbital or prefrontal process ; p.f., postfi-oiital process ; sq., squamosal 



s.m., suprameatal tubercle. 



From the hinder border of the orbit a process projects down- 

 wards and forwards which we may call ihepostorhital., or, as I prefer 

 to call it, the postfrontal process : ic is also called by Dr. Mivart ' 

 the sphenotic process. I may remark that this is only one of 

 many cases where we remain in doubt as to what nomenclature to 

 use, "for want of knowledge of the facts of embryology. Parker, 

 in his account of the Fowl's skull ^ where this process is not unlike 

 that of many Parrots, describes its development from a separate 

 element, the postf rental, and it certainly seems to me, from a 

 study of such material as I possess, to be developed both in the 

 Powl and in Eatites from a frontal or postfrontal element, with 

 which a process of the aUsphenoid may be associated. It_ is 

 sometimes ascribed, as by Gadow ^ to the squamosal bone, which 



1 Mivart, Skeletons of Lorius and Psittacus, pt. ii., P. Z. S. 1895, p. 3(iy. 

 '■" Parker, Phil. Trans. 1869, pt. ii. p. 790. 

 •^ Gadow, Newton's Diet, of Birds, p. 873. 



