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Show 220 ON THE STRUC'fURE OF '!'HE SKULL. The combination of peculiarities just mentioned at once characterises the skulls of Birds and Reptiles, and distinguishes them from all others. In all these anirnals, the basi-occipital bone gives attach-ment to a pair of ex-occipitals, which articulate, above, with a distinct supra-occipital. The homology of these bones with those which have received similar names in the Man's and in the . Pike's skull is not doubted; and, indeed, their relations to one another, and to the exits of the eighth pair, are so similar as to allow of no discussion on this point. Furthermore, the skulls of all Reptiles and Birds are roofed in by membrane bones, the correspondence of which with the parietals and frontals of Man is universally admitted; and, in all, there is a single or a double vomer, clearly identifiable with· that of the Man and that of the Fish. So, again, there is no doubt about the homology of the premaxillre and the maxilla;, the palatine. and the pterygoid bones with the parts so named in Man. Nor is it _questioned that the mandible and the hyoidean arches, in a general way, correspond with his. But there has been, and is, very great divergence of opinion as to the true nature of certain bones in the side walls of the skull, and of some of those which enter into the composition of the maxillary apparatus. I shall address myself chiefly to the discussion of these debatable ossifications. The bone of most importance among these (the misinterpre-tation of which must needs, indeed, completely vitiate and render worthless any theory of the vertebrate skull) is that which lies in the side wall of the cranium, in front of the exoccipital; while it is connected below with the basi-sphenoid, and above with the supra-occipital and parietal. In all BiJ:ds tians, Monitors, Chelonians, Crocodiles, and in all kinus of Birds." Mr. Parker agrees with my suggestion (supra, p. 170), that the basi-temporals of the Sauropsida (or Birds and Reptiles) arc tho homologue of tho ling~ sphenoidales of Man. He bas found similar bones in numerous Mammals, and they are of especially large size in the Mole and in the Shrew. He informs me that tlle Sheep bas no bony centre for the basi-sphenoid, the alisph noids meeting in the middle line. Nevertheless its lingulte arc well developed at the commencement of the last tllird of intra· uterine life. 00 00 |
