DE. J. MURIE ON THE FOEM AND STEUCTUEE OF THE MANATEE. 1G7 



Of the fossil genus Halitherium, besides other observers, the vahiable researches of 

 Professors Kaup and Krauss prove its being furnished with a full complement of molar 

 teeth and tusks, as in Ilalicore. 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 li\dng 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 SteUer upon an important point, viz. the 

 structure of the palatal and mandibular laminae. These SteUer 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, Ghhiocejohalus 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 III. September, 1872. 2 c 



