DR. J. MURIE ON THE FORM AND STRUCTURE OF THE MANATEE. 167 
Of the fossil genus Halitherium, besides other observers, the valuable researches of 
Professors Kaup and Krauss prove its being furnished with a full complement of molar 
teeth and tusks, as in Halicore. From the construction of the palate, intermaxillaries, 
and symphysial portion of mandible, I think we are justified in believing it was also 
provided with horny plates akin to those of the living Sirenia. This granted, a hairy 
and possibly a full, truncate muzzle may likewise have characterized it. 
On carefully studying Steller’s admirable description of the muzzle and interior of 
the mouth of the now extinct northern Rhytina, I have been struck with the similitude 
to that of the Manati examined by myself. Indeed, excepting in size, slight variation 
of the rasping-plates, and absence of teeth, what he says perfectly accords with the 
formation of parts in the latter species. 
It has been reserved for the very able and learned Professor Brandt, of St. Peters- 
burgh, to correct the otherwise accurate Steller upon an important point, viz. the 
structure of the palatal and mandibular lamine. These Steller regarded as two 
osseous plates, not true teeth, but rather as it were supplying the place of these in 
mastication. But although their function may undoubtedly have been trituration of 
the food, still Brandt, after a very elaborate microscopic examination, has satisfactorily 
demonstrated their indurated epithelial character, quite wanting in bony or dental 
substance. 
Steller’s figures of them when removed convey but a hazy impression of what they 
must have appeared when in the mouth. Brandt’s illustration of the palatal plate in 
situ, however, enables a clearer conception and estimate of it to be made. From this, 
and what he himself states, the structure in question can be no other than the homo- 
logue of that found in Manatus and Halicore. It certainly does not appear to me to be 
the representative of teeth, nor of the baleen plates met with in the true Cetacea (an 
idea some are disposed to accept). Although Rhytina was edentulous in the adult condi- 
tion, I strongly suspect that, like the other Sirenian genera, rudimentary teeth may have 
existed in its earlier stages of growth. Nordmann seems favourably inclined to this 
opinion. The maxillary alveolar ridges are narrow and quite behind the bruising 
plate, the latter occupying the intermaxillary and not the maxillary bones. 
Among Cetacea the toothed and whalebone groups necessarily present differences. 
As exemplifying the former, Glodiocephalus has no hairy bristles on the snout or 
within the lips—these parts superficially exhibiting a moderately smooth, tough, jet- 
black membrane. The alveoli are well defined, and the gum-tissues highly ridged 
betwixt the numerous teeth. The front V-shaped arch formed by the junction of the 
upper gums is callous, and evidently homologous with the front pad or inner upper 
lip already alluded to. The anterior third of the membrane of the hard palate is dense 
and fibrous beneath, and beset with irregular rows of hardened, closely placed excres- 
cences; posteriorly the roof of the mouth is smoother and of a lighter colour. The 
anterior part, therefore, in external appearance and structure, is the homologue of the 
VOL. VIII.—PaRT UI. September, 1872. 2c 
