144 ^^^^ SKULL. [CHAi'. 



the anterior arch, and the basihyal in the form of a narrow 

 transverse bar. 



Some of the Lemuriua have much shorter faces than the 

 common species, though still possessing all the essential 

 characters of the group. Among these, Tarsius is remark- 

 able for the extraordinary size of the orbits, which are so 

 expanded that their margins form prominent, thin, bony 

 rings, and the interorbital part of the skull is reduced to 

 an exceedingly delicate septum. The orbit is also partially 

 separated from the temporal fossa as in the Simiina. 



The general characteristics of the skull of the Carxivora 

 have been described, as seen in the Dog. The more obvious 

 modifications from this type relate to the comparative 

 length and compression or width of the facial portion, the 

 strength and curve of the zygomatic arch, and the extent to 

 which the various ridges and processes for the attachment 

 of muscles are developed. Thus the Cats have short and 

 round skulls, with wide zygomatic arches ; and in the Bears 

 (especially the Polar Bear, Ursus inaritimus) the whole 

 skull is elongated, and the nasal cavities are greatly enlarged 

 as compared with the brain- case, and the maxillo-turbinal 

 bones are correspondingly developed. 



But there are certain other modifications of the cranial 

 bones, which, being less obviously adaptive to functional 

 purposes, and being constantly associated with structural 

 modifications in other parts of the body, are of considerable 

 value in classifying the members of the group. Of these 

 the most important are related to the form and structure of 

 the auditory bulla, and the surrounding parts of the base of 

 the cranium. 



In the Bears, the auditory bulla is comparatively little 

 inflated. It consists of a single bone (tympanic), readily 



