631 



weed, in the stomach. The canine tusks serve as weapons of offence and defence, and to 

 aid the animal in mounting and clambering over blocks of ice in the Polar seas which it 



frequents. 



Presented by Colonel Sabine, R.E. 



3861. The skull of a male Walrus (Trichecus Rosmaru*). 



The canine tusks are nineteen inches and a half long, measured from the rim of the alveo- 

 lus. The superoccipital inclines a little upwards and forwards, is divided by a median crista, 

 and is bounded above by a broad rugged tract. The paroccipitals are broad, but not very 

 prominent : the hinder surface of the skull is much extended laterally by the great develop- 

 ment of the mastoids. The zygomatic process of the squamosal is remarkably thick. The 

 molar sends up a lofty postorbital process : the maxillary developes a large but low sub-bifid 

 antorbital process. There is a large oval vacuity in the lateral walls of the posterior nares. 

 The skull is singularly expanded, short, obtuse, and as it were truncated anteriorly, and, being 

 constricted between the orbits, the upper surface presents an hour-glass form. The thick 

 parietes of the cranium have been laid open on the right side, exposing the cranial cavity. 

 The bony tentorium, the large and shallow sella turcica, with anterior and posterior clinoid 

 processes, and the prominent crista galli, may be noticed. Most of the sutures of this cra- 

 nium have become obliterated. The basioccipital is subcarinate below. The petrosal termi- 

 nates below in three obtuse processes, but there is no bulla ossea. The pterygoid process is 

 perforated by the ectocarotid. The bony roof of the palate is very concave towards the 

 mouth, and terminates behind by a broad biangular notch. There are four molar teeth on 

 each side of the upper jaw, worn down obliquely, as usual, to nearly the level of their alveoli. 

 There is no trace of incisors or their sockets. The lower jaw is thick and massive : the rami 

 are confluent at the symphysis, with short obtuse angular tuberosities, and with the condyles 

 on a level with the lower border. The last molar on the outside has been shed. 



Presented by the Lords of the Admiralty. 



'^(\'l. The skull of a larger and older male Walrus (Trichecus Rosmarus). 



It shows the great development of the mastoids, and the well-marked ridge dividing the 

 nasal and maxillary from the smoother frontal surface. Behind the four upper molars there 

 is the socket of a smaller fifth tooth on the right side. There is a corresponding fifth small 

 socket on each side of the lower jaw. 



Presented by the Lords of the Admiralty. 



3863. The skull of an old male Walrus (Trichecus Rosmarus}. 



The remains of an incisor are seen in the right premaxillary, and behind the four ordinary 

 molars there is the socket of a fifth small molar on each side of the upper jaw, and a sixth still 

 smaller socket on the left side. The lower jaw shows only the ordinary four molars on each side. 



Presented by the Lords of the Admiralty. 



3864. The mutilated cranium of a very large male Walrus (Trichecus Rosmarus). 



The margin of* the foramen magnum has been sawn off, exposing the lateral sinuses. The 



