456 im. R. BROOM ox the 



liomologiie of the reptilian paired vomer ; and it cannot be the 

 septomaxillary. It is no doubt the same bone as Parker found 

 in a number of mammals and referred to as the postero-lateral 

 vomer ; but it is no pai-t of the true vomer. Considering how- 

 very large a membranous ossification is formed in connection, as 

 we shall see, with the basisphenoid, one may think of the jDOSsibility 

 of this being a membranous exostosis in connection with the 

 presphenoid, though at this stage, and even in the later one 

 represented by the small skull dissected, there is no ossification 

 of the cartilaginous presphenoid. In the meantime I think it 

 safest to leave the significance of the bone as very doubtful. 



The alisphenoid is fairly well developed but very narrow, and 

 much more like a columella cranii than in any other mammal 

 I know. It is still mainly cartilaginous, though commencing to 

 ossify along the posterior border, and at its inner end there is 

 considerable ossification which cannot altogether be separated 

 from the ossification in membrane which is spreading out from 

 the basisphenoid. 



The basisphenoid is chiefly remarkable for the large mem- 

 branous exostosis which forms a large process extending down- 

 wards and outwards. This process may be regarded as a 

 basisphenoidal process comparable to the basisphenoidal pro- 

 cess of many reptiles in having a true articulation with the 

 pterygoid. 



The auditory ossicles are relatively large. 



The general structure of the auditory region will be more 

 readily understood from the sections. The tegmen tympani is 

 feebly developed. 



The most interesting feature of the occiput is the fact that 

 only a relatively small part of the supraoccipital is preformed 

 in cartilage. The greater part is a membranous exostosis which 

 fi.lls in the median portion between the two sides. It might be 

 argued that this median part is really the interparietal, but from, 

 the condition seen in the later states it seems better to look on 

 the ossification as a supraoccipital in which only the lateral paints 

 have a cartilage basis. 



Description of the more important sections. 



As I have in my previous paper figured and described the 

 cartilages in connection with Jacobson's organ, and as the 

 posterior part of the nasal capsule has a very complicated 

 arrangement of turbinals which would require for the complete 

 solution of its significance a much fuller comparison with other 

 mammalian types than is at present possible, I shall leave any 

 detailed account of the nasal cartilages till some future time. 



Figures 1^6 (PI. I.) represent sections 131, 185, 238, 280, 302, 

 and 316 respectively, and show the general arrangement of the 

 nasal cartilages. 



Fig. 1, which is through the middle part of Jacobson's organ. 



