DE. J. MTJEIE ON THE FORM AND STEUCTUEE OF THE MANATEE. 169 



numerous conical papillfe, elevations of the mucous membrane, which find their counter- 

 part in the trapezoidal ridges of the Manatee, between which the hairs and bristles 

 sprout. Furthermore, from Eschricht and Reinhardt's statement that the soft portion 

 of the baleen is only an excessively developed condition of mucous membrane and epi- 

 thelial cells, it may be presumed that the ruminant papillae and the identical structure 

 in the mouth of Sirenia are the homologous constituents of the Cetacean gum. Con- 

 tinuing the comparison of parts, the pad behind the lower incisors in the Sheep accords 

 with the symphysial pad in the Manatee, and the fringe of roughened skin-texture on 

 the edge of the lower lip of the former with the broader, thicker, semilunar patch in 

 the latter. Both have a hairy muzzle and beard ; and the cleft tendency of the upper 

 lip in Ovis recalls the wider, semilunar, truncated muzzle of Manatus. 



Lastly, if the oral cavity of Pachyderms be considered, homologous parts are dis- 

 cernible. In Eleplias the palatal pads are much softer and smaller in proportion than 

 in the Lamatins, the muzzle is elongated into a prehensile trunk, the lower lip is like- 

 wise lengthened. But long bristly hairs are largely developed within the buccal region, 

 especially in the African Elephant. 



From the facts which have been particularized, I think that with some show of reason 

 the following inferences may be drawn : — 



1st. That the upper horny masticating-plate of Manatus is homologous with the 

 roughened, warty, or retroverted papillary portion of the palate of Cetacea, Ruminantia, 

 Pachydermata, &c. 



2nd. That the horny baleen plates of Cetacea find their homologue in the Sirenia 

 and some Pachydermata, in those developments of hairs and bristle-strips within the 

 mouth and cheeks, existing either in bunches or as more separate filaments. 



3rd. That the folds of mucous membrane within the inner upper lip of the Sirenia 

 are represented by buccal papillae in Ruminants and other forms, and that the greater 

 development of similarly constituted mucous membrane in the interior of the mouth of 

 some Cetaceans forms the intermediate substance of the baleen. 



2. Alimentary Canal. 

 Beyond the constrictor muscles of the pharynx to within an incli of the stomach, the 

 oesophagus is very narrow, not large, as it is said to be in Rhytina\ being no more than 

 half an inch in diameter in the ordinary undistended condition. But its muscular 

 walls are uncommonly thick at its lower end, agreeing in this respect with the Dugong, 

 as mentioned by Owenl There is an outer layer of longitudinal fleshy fibres, and 

 beneath that the usual decussating oblique layers. For eight inches or more in the 

 female specimen the average thickness of the walls was a little over O'l inch; the 

 relative depth of the cuticular and submucous lining to the fleshy fibre lining is as one 

 to two. Near and at the cardiac orifice, however, the muscular covering increased 

 ' Steller, op. cit. p. 310. > P. Z. S. 1838, p. 30. 



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