106 
ing rather to the same (premolar) series, than as being the first of 
the true molars. As the first of the molariform permanent teeth in 
the lower jaw passes in front of the permanent incisor above, when 
the mouth is closed, it must be regarded as an ‘incisor’; the other 
three grinders as being ‘premolars’, two being proved to be such by 
displacing vertically their predecessors, and the third also appearing 
to be of the same series by its state of development. The Professor 
accordingly proposed the following as the formula of the normal or 
functional dentition of the Walrus :— 
i, cS, p= 18. 
But, as might be expected in a dentition deviating so remarkably from 
that of other Mammals of the same order, varieties are not unfre- 
quently met with in the number of the teeth of the Walrus. Pro- 
fessor Owen cited instances of such varieties in ten skulls of the 
Walrus, of different ages and sex. The result of which was, that 
occasionally a small tooth was found anterior to the normal series of 
four, and more commonly in the upper than in the lower jaw; and 
that, more rarely, a small tooth was superadded behind the normal 
four, in the upper jaw, and still more rarely in the lower jaw: the 
formula of the dentition of such varieties, in excess, being,— 
- 2-2 1—1 3—8 196. 
= 
@ 99?) © Gan ae pemre = e 
The additional anterior small incisor was due either to the reten- 
tion and growth of the first deciduous denticle, or to the develop- 
ment of a small successor to it. The additional posterior grinder was 
due to the occasional development of a germ in the back part of the 
gum or jaw. The minute milk-teeth relate, by their gubernacula, to 
the development of the permanent teeth, but seem never to be put to 
use themselves ; the milk-canine was buried in the gum outside the 
protruded point of the permanent canine ; so that this tooth is extri- 
cated and cuts the gum before the tooth of which it is the successor 
makes its appearance, that tooth being probably removed by absorp- 
tion. Here, therefore, was another instance, analogous to that of the 
rudimental teeth in the foetal Whale, of parts developed without any 
obvious office as organs of mastication, but serving to illustrate the 
relation of adhesion to a more normal type of dentition. In conclu- 
sion, Professor Owen remarked that the food of the Walrus consisted, 
in a state of nature, of sea-weed, crustaceans and mollusks; and that 
although, by the totality of its organization, it must be placed near 
the Seals, and with them be classed in the order Carnivora, yet that 
the incisors and premolars were alike well adapted to pound marine 
plants, and to break and crush shells. Fragments of a bivalve shell, 
a species of Mya, had been found with pounded sea-weed, by the 
Surgeon of Parry’s Polar Expedition, in the stomach of a full-grown 
Walrus. The great descending. canine tusks serve as weapons of 
offence and defence, and to aid the animal in mounting and clamber- 
ing over ice-blocks, bergs and floes in the Arctic Seas, in which the 
Walrus has been organized to enjoy its existence. 
