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Show 10 PROF. D'ARCY 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 m y own collection, which is considerable, and partly from skulls belonging to the Royal 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 4he skull and quadrate of Psittacus erithacus (figs. 1 & 2) show the characters to which attention will be chiefly drawn in the descriptions. Fig. 1. Psittacus erithacus. pr.o., preorbital or prefrontal process ; p.f., postfrontal process; sq., squamosal s.m., suprameatal tubercle. From the hinder border of the orbit a process projects downwards and forwards which we may call thepostorhital, or, as I prefer to call it, the postfrontal process : it is also called by Dr. Mivart1 the sphenotic process. I may remark that this is only one of many cases w7here we remain in doubt as to wdiat nomenclature to use, for want of knowledge of the facts of embryology. Parker, in his account of the Fowl's skull2, where this process is not unlike that of many Parrots, describes its development from a separate element, the postfrontal, and it certainly seems to me, from a study of such material as I possess, to be developed both in the Fowl and in Ratites from a frontal or postfrontal element, with which a process of the alisphenoid may be associated. It is sometimes ascribed, as by Gadow 3, to the squamosal bone, which 1 Mivart, Skeletons of Lorius and Psittacus, pt. ii., P. Z. S. 1895, p. 363. 2 Parker, Phil. Trans. 1869, pt. ii. p. 790. 3 Gadow, Newton's Diet, of Birds, p. 873. |