633 



of the parietals, and its termination in the longitudinal sinus may be traced. The bony 

 tentorium terminates above the base of the petrosal ; a thick, smooth ridge has entered the 

 lower half of the fissure between the anterior and posterior cerebral lobes. A similar but 

 shorter ridge from the inner side of the frontal more completely defines the rhineneephalic 

 chamber. The left ramus of the lower jaw has been fractured, and had become the seat of 

 caries during the lifetime of the animal. The right moiety exposes the inner surface of the 

 large and complex turbinals : an elliptic foramen, three lines by five, leads from the lower 

 and outer corner of the rhinencephalic fossa into the back part of the orbit between the 

 orbitosphenoids and frontals. The venous fossa on the inner side of the condyles is divided 

 by a bony bar in both sections. The natural contour of the wide sphenopalatine vacuity is 

 well seen in this skull. 



Hunterian. 



3869. The skull of a Walrus (Trichecus Rosmarus). Hunterian. 



3870. The skull of a Walrus (Trichecus Rosmarus). Hunterian. 



3871. The skull of a Walrus (Trie-keens Rosmarus). Hunterian. 



3872. A longitudinal section of the cranium of a Walrus (Trichecus Rosmarus), in 

 which the bony tentorium, the cribriform plate of the aethmoid bone, &c., are 

 shown. Hunterian. 



3873. A transverse section of the cranium of a young Walrus (Trickecus Rosmarus), 

 showing the bony tentorium. Hunterian. 



3874. The skull of a young male Walrus (Trickecus Rosmarus). 



The remains of the sutures show that the alisphenoid is excluded from the parietal by the 

 junction of a small part of the frontal with the squamosal on both sides. There is no trace 

 of a lacrymal bone, but a small elliptical canal perforates the base of the antorbital process 

 of the frontal slightly upwards. The maxillary portion of the skull is less broad in proportion 

 to the cranial part than in the older Walruses. There is a small incisive socket and a rudi- 

 ment of a tooth on the left side, anterior to the first of the four normal molar teeth, and the 

 point of this tooth is just appearing, whilst the crowns of the three others are obliquely 

 worn : there is a small socket behind the four normal molars of the lower jaw ; that on the 

 left side contains a rudimental tooth. 



Presented by the Lords of the Admiralty. 



4 M 



