THE SKELETON OF THE VERTEBKATE HEAD. 165 



called " vomer," and as those of the lizard, serpent, and frog to 

 the bones hitherto called " palatal " in these three forms. I 

 therefore apply provisionally the term ento-pterygoid to the 

 so-called " vomer " of the bird, to the posterior part of the so- 

 called " vomer " of the chelonian, to the corresponding bony 

 piece in the crocodiles, to the so-called "palatals" of the 

 ophidian, lacertian, and batrachian, to the " bones of Bertin," 

 and their representatives in the mammal. 



The Constitution of the Nasal Fossae, and the Relative Posi- 

 tions of the External and Internal Nares. The details necessary 

 for the morphological examination of the rhinal, vomerine, 

 ethmoidal, and pre-sphenoidal sclerotomes, have involved a 

 number of facts connected with the varied constitution of the 

 nasal fossae in the different vertebrate forms. As, however, 

 the constitution of these fossae has important bearings on the 

 morphology of the entire cranium, I shall briefly direct atten- 

 tion to the subject. 



The only perfect form of nasal fossae is that presented by 

 the mammal. They consist of the entire neuro-haemal cavities 

 of the rhinal and vomerine, combined with the haemal cavities 

 of the ethmoidal and pre-sphenoidal sclerotomes. That portion 

 of the combined nasal fossae which consists of the cavities of 

 the rhinal and vomerine sclerotomes, is divided in the mesial 

 plane by the centrums of those sclerotomes ; while the 

 dependent portion of the ethmoidal centrum, and the posterior 

 portion of the vomerine centrum, divide in the same manner 

 that part of the combined fossae which consists of the haemal 

 cavities of the ethmoidal and pre-sphenoidal sclerotomes. The 

 mammalian nasal fossae are therefore bounded in front by the 

 walls of the neuro-haemal chambers of two catacentric sclero- 

 tomes ; and posteriorly by the catacentrically divided haemal 

 chambers of a demicatacentric and diacentric sclerotome. 



As the haemal portions of the cephalic somatomes are 

 separated from one another in their early embryo condition by 



