220 OX THE STRUCTURE OF THE SKULL. 



The combination of peculiarities just mentioned at once cha- 

 racterises the skulls of Birds and Beptiles, and distinguishes 

 them from all others. 



In all these animals, 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 preruaxillae and the maxillae, 

 the palatine and the pterygoid bones with the parts so named 

 in Man. Nor is it questioned that the mandible and the hyoi- 

 dean 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 w r all of the cranium, in front of the ex- 

 occipital ; while it is connected below with the basi-sphenoid, 

 and above with the supra-occipital and parietal. In all Birds 



tians, Monitors, Chelonians, Crocodiles, and in all kinds of Birds." Mr. Parker 

 agrees with my suggestion (supra, p. 170), that the basi-teraporals of the Sauropskla 

 (or Birds and Reptiles) are the homologues of the lingulx sphenoldales of Man. He 

 has found similar bones in numerous Mammals, and they are of especially large size 

 in the Mole and in the Shrew. He informs me that the Sheep has no bony centre 

 for the basi-sphenoid, the alisphenoids meeting in the middle line. Nevertheless 

 its liucjidx are well developed at the commencement of the last third of intra- 

 uterine life. 



