50 ODOB^ENUS ROSMARUS ATLANTIC WALRUS. 



traces of alveoli of six incisors both above and below, and to 

 the early deciduous character of the last (fifth) upper molar, 

 and the frequent disappearance of the fourth. He concludes 

 that the normal number of the back-teeth is |^|, and that in 

 early life the dentition of the Walrus is not widely different from 

 that of other Pinnipeds. 



The same year (1838), Macgillivray* considered the normal 

 dentition of the Walrus to be I. 5|; 0. ^5 Pm. + M.^ 

 =^| = 32. His conclusion was based on the examination of a 

 quite young specimen, of which he speaks as follows: "The 

 normal dentition of the Walrus is shown by the skull of a young 

 individual in the Museum of the Edinburgh College of Surgeons. 

 In the upper jaw there are on each side three incisors, the first 

 or inner extremely small, the second a li ttle larger, the third or 

 outer disproportionately large, being equal to the larger grind- 

 ers. The socket of this tooth is placed in the intermaxillary 

 bone, but towards its mouth it is partly formed by the maxillary. 

 The small incisors have deep conical sockets. The canine 

 tooth is displaced, being thrust outwards beyond the line of the 

 other teeth, and causing the peculiar bulging of the head. The 

 lateral incisor is on the level of its anterior margin, and the 

 first grinder is opposite to its middle. There are five grinders, 

 having conical obtuse sockets, and consequently single roots ; 

 the first smaller than the last incisor, the second and third 

 largest, the fourth much smaller, the fifth very small, all 

 shortly conical, and blunt, with enamel on the tip only. The 

 canine tooth is also at first enamelled at its extremity. In the 

 lower jaw there are two very small conical incisors on each 

 side 5 the canine tooth is wanting $ five grinders, with single con- 

 ical compressed roots, and short compressed conical crowns, 

 enamelled at the point; the first, second, and third nearly equal, 

 the latter being a little larger, the fourth much smaller, and 

 the fifth very small. The tusks, or enormously developed 

 canine teeth of the upper jaw, are compressed, conical, a little 

 curved backward, directed downwards and a little forwards, and 

 somewhat diverging, but in some individuals, w^hen very long, 

 they again converge towards the points. In adults, the incisors 

 are obliterated, excepting the lateral pair of the upper jaw; the 

 fifth grinder in both jaws has also disappeared, and sometimes 

 the fourth in one or both jaws." 



* British Quadrupeds, 1838, pp. 220, 221. 



