THE SKELETON IN MAMMALIA. THE SKULL. 461 



genera, in all of which they are curiously bent down in front. 

 Their upper margin forms the anterior border of a very large 

 aperture lying high on the roof of the skull and extending 

 back for a considerable distance. This aperture is formed by 

 the union of the two anterior nares. The nasals are quite 

 vestigial or absent, and the iiarial aperture is bounded above 

 by the frontals; in its floor are seen the slender vomer and 

 large mesethmoid. The palate is long and narrow, and formed 

 mainly by the maxillae ; behind it there is a large irregular 

 process formed by the union of the palatine, pterygoid, and 

 pterygoid plate of the alisphenoid. The mandible is very 

 massive and has a very high ascending portion, a rounded 

 angle (fig. 92, 10), and a prominent coronoid process ; the two 

 rami are firmly ankylosed together. The hyoid consists prin- 

 cipally of the broad flat basi-hyal ; the anterior cornua are but 

 slightly ossified, while the thyro-hyals are not ossified at all. 



CETACEA. The skull in all Getacea, especially in the Odon- 

 toceti, is a good deal modified from the ordinary mammalian 

 type. 



In the ARCHAEOCETI this modification is less marked than 

 in either of the other suborders. The nasals and premaxillae 

 are a good deal larger than they are in living forms, and the 

 anterior nares are placed further forward. The maxillae do 

 not extend back over the frontals, and there is a well-marked 

 sagittal crest. 



In the MYSTACOCETI the skull is always quite bilaterally 

 symmetrical, and is not so much modified from the ordinary 

 mammalian type as in the Odontoceti. The parietals are not, 

 as in the Odontoceti, separated by a wide interparietal, but 

 meet ; they are, however, hidden under the very large supra- 

 occipital. The nasals are developed to a certain extent, and 

 the nares, though placed very far back and near the top of the 

 head, terminate forwardly-directed narial passages. Turbinal 

 bones are also developed to some extent ; this fact, and the 

 occurrence of a definite though small olfactory fossa constituting 



