214 SI RENT A 



owing to the very oblique position of the diaphragm, the thoracic 

 cavity extends far back over the abdomen. The epiglottis and 

 arytenoid cartilages of the larynx do not form a tubular prolong- 

 ation as in the Cetacea, so that the epiglottis is not intranarial. 

 The brain is of comparatively small size, and the convolutions on 

 the surface of the cerebrum are few and shallow. The kidneys are 

 simple. The testes abdominal. The uterus is bicornuate. The 

 placenta (in the Dugong) is non-deciduate and zonary. The um- 

 bilical vesicle disappears early. The mammae are two, and pectoral, 

 or rather post-axillary in position. 



The Sirenia pass their Avhole life in the water, being denizens of 

 shallow bays, estuaries, lagoons, and large rivers, but, unlike the 

 Cetacea, are not met with in the high seas, far away from the shore. 

 Their food consists entirely of aquatic plants, either marine algse or 

 freshwater grasses, upon which they browse beneath the surface, as 

 the terrestrial herbivorous mammals do upon the green pastures on 

 shore. They are generally gregarious, slow and inactive in their 

 movements, mild, inoffensive, and apparently unintelligent in dis- 

 position. Though occasionally found stranded by the tide or waves, 

 there is no satisfactory evidence that they voluntarily leave the water 

 to bask or feed on the shore. The habit of the Dugong of raising 

 its round head out of the water, and carrying its young under the 

 fore fin, seems to have given rise, among the imaginative early 

 voyagers in the Indian Ocean, to the legendary beings, half human 

 and half fish, in allusion to which the name Sirenia was bestowed by 

 Illiger on the order, though certainly the face of a Dugong, when 

 closely inspected, does not bear the slightest resemblance to that of 

 the mermaid of romance. The species now existing are very few, 

 and there is reason to believe that the time is not far distant when 

 they will all become extinct. One species, Rhytina stdleri, of the 

 North Pacific, was totally exterminated through the agency of man 

 during the last century ; and the others, being valuable for their 

 flesh as food, for their hides, and especially for the oil obtained from 

 the thick layer of fat which lies immediately beneath their skin, 

 rapidly diminish in numbers as civilised populations occupy the 

 regions forming their natural habitat. The surviving species are 

 confined to the tropical regions of the shores of both sides of the 

 Atlantic and the great rivers which empty themselves into that 

 ocean, and to the coasts of the Indian Ocean from the Red Sea to 

 North Australia. In the Miocene and early Pliocene epoch 

 Sirenians abounded in the seas of Europe, and their remains 

 have been found in deposits of corresponding periods in North 

 America. Evidence has also been discovered of the existence 

 of an animal of this group in the seas at the bottom of which 

 the Eocene nummulitic limestone mountain ranges of Egypt were 

 deposited. 



