652 



3983. The skull of a male Polar Bear (Ursus maritimus). 



It is of equal size with the preceding, but is from a younger animal, and shows the sutures 

 of the cranium. The commencement of the sagittal crest is here seen to be two inches in 

 advance of the coronal suture : the posterior points of the nasals extend much further back 

 than the nasal processes of the maxillaries. The premaxillaries join the frontals. A vertical 

 section of the cranium has been made, showing the bony tentorium and the ridge which pene- 

 trates the fissura magna sylvii. There are two small premolars (p 1 & p 3) on each side of 

 the upper jaw, and one premolar (p 1) on each side of the lower jaw, between the canine and 

 the last or constant premolar (p4). 



Mm. Brit. 



3984. The skull of a male Polar Bear (Ursus maritimus). 



The occipital condyles are mutilated. It shows the same state of the rudimental pre- 

 molars as in the preceding specimen. 



Hunterian. 



3985. The skull of a young, but nearly full-grown, Polar Bear (Ursus maritimus). 



The first and third premolars are present on both sides of the upper jaw and on the left 

 side of the lower jaw, the first only being retained on the right side. The occipital condyles 

 have been sawed off. 



Presented by the Lords of the Admiralty. 



3986. The skull of a young, but nearly full-grown, Polar Bear (Ursus maritimus). 



The sockets of the three rudimental premolars are present between the canine and last pre- 

 molar on both sides of the upper jaw, but the first rudimental premolar only remains in the 

 lower jaw. 



Presented by William Gaitskell, Esq. 



3987. The skull of a young Polar Bear (Ursus maritimus). 



Of the rudimental premolars the sockets of p 1 and p 3 are present on both sides of the upper 

 jaw ; those of p 1 and p 2 are present on the left side of the lower jaw, but the socket of p I 

 only remains on the right side. 



Presented by Sir William Blizard, F.B.S. 



3988. The cranium, in three transverse sections, of a Polar Bear (Ursus maritimus). 



The hindmost has been made through the middle of the mastoid process, and includes the 

 epencephalic division of the cranial cavity, with part of the acoustic cavities. It well exhibits 

 the cerebellar fossse, formed by the bony tentorium above, and by a shorter osseous ridge 

 below separating the cerebellum from the upper part of the medulla oblongata. The com- 

 mencement of the entocarotid canal may be seen distinct from the fore part of the fossa jugu- 

 laris, and the division of the petrosal fossa into two cells for the reception of the cerebellar 



