LECT. III.] THE HARD PALATE. 75 



vomerine series of bones have behind them, under 

 the main skull, another series, namely, the "para- 

 sphenoid" and its divisions. This series, as I shall 

 .afterwards show, appears in the Mammalia, and the 

 .arrangement is always as one, two, or three a recollec- 

 tion, so to speak, of the primary pattern of median and 

 sub-median bones in the lowest Ganoid Fishes. In the 

 mammals, generally, during the embryo stage, there 

 .are five vomers, but in Marsupials there may be ten. 



Character 2. The bony palate is deficient in the 

 Hedgehog and other low Eutheria, and is very limited in 

 the lower Eodents. Such a specialisation of the cheek 

 and palate bones is only rudimentary in the Amphibia, 

 in Serpents, and in Lizards ; in the larger Chelonia 

 (Turtles) it is very considerable, while in the Crocodile, 

 as in some of the lowest Eutheria, e.g., Ant-eaters, it 

 attains its utmost development. In birds, which, more 

 than any other group, lie away from this line of descent, 

 this structure is very slightly developed. 



Character 3. This character, the hollo wness of the 

 squamous part of the temporal bone, is very marked in 

 the lower Eutheria, such as Edentates and Insectivora. 

 In the tailed Amphibia there is no drum-cavity ; in the 

 tail-less kind, where it is generally present, I never saw 

 this cavity enlarged by extension of the air-cell into the 

 neighbouring bones. Nor in Serpents or Lizards is 

 there any excavation of the bones in this part ; the 

 former have no drum cavity, most of the latter have. 



