500 



ANATOMY OF VERTEBRATES. 



Grisly Bear ( Ursus ferox), the facial part of the skull is re- 

 latively longer than in the Ursus arctos, and the nasal processes 

 of the premaxillaries are much longer, are more slender, and ar- 

 ticulate directly with the anterior processes of the frontals. In 

 the Brown Bear, the maxillaries articulate with the small part of 

 the nasals and separate the premaxillaries from the frontals. In 

 the Polar Bear ( Ursus rnaritimus, fig. 340), the lower extremities 

 of the occipital condyles are united hy a ridge, which, however, 

 is less prominent than in the Ursus ferox. The precondyloid 

 foramen is exposed. The superoccipital, 3, terminates above in a 

 strong ridge overhanging the condyles. Both paroccipitals, 4, 

 and mastoids, 8, are well developed, but the latter are the larger 



340 



processes. The temporal ridges, commencing at the postorbital 

 processes, converge at a right angle and meet at about two 

 inches behind the orbits, and form a long and prominent sagittal 

 crest, the upper border of Avhich is straight ; the frontal region 

 is low and flattened. Within the cranium the cerebellar fossa is 

 formed by the bony tentorium above, and by a shorter osseous 

 ridge below, separating the cerebellum from the upper part of the 

 medulla oblono-ata. The commencement of the entocarotid canal 

 may be seen distinct from the fore part of the fossa jugularis ; the 

 petrosal fossa is divided into two cells for the reception of the 

 cerebellar appendages. The mastoid is occupied by a close 

 diploe, which receives no air-cells from the tymjoanic cavity. 

 The meatus auditorius terminates obliquely within the tympanic 

 cavity. A triangular constriction separates the prosencephalic 

 from the rhinencephalic chamber. The malar, 26, alone forms the 

 postorbital rising : the squamosal, 27, does not reach so far ; 

 it developes a low subquadrate cranial plate, r/. The mandible 



