49 



external conclies, and orifices extremely smaU ; eyes sma]l, provided 

 with nictating membrane ; mammsB two, pectoral ; voice reduced to a 

 feeble lowing ; no dorsal fin or protuberance. 



Of tbe skeleton, the bones are of dense texture, like ivory, and not 

 loaded witb oil ; nasal aperture expanded, placed high up on the 

 cranium ; cheek bones massive ; occipital condyles terminal ; cervical 

 vertebreeseparate ; costo-stemal ribs cartilaginous ; sternum composed 

 of one piece ; pelvis small, or rudimentary ; caudal regions elongated, 

 possessing true V-shaped bones beneath their anterior vertebrse. 



In habits the existing Sirenoida are gregarious, monogamous, (?) 

 sluggish, usually frequenting shallow waters, and vegetarians in their 

 diet. 



The extant forms of this order are included within three well-defined 

 genera, of which the species of two of them reveal, in their cervical 

 vertebrsB, a marked numerical deviation from the ordinary mammalian 

 type, the three-toed sloth furnishing the only other exception to the 

 general rule. In the Sloth these joints amount to nine, while in the 

 present animals they number only six. 



Family MANATIDiE.^ 



(a) Genera Des'tata. 



Teeth various in number ; incisors large, conical, or, very small, early 

 deciduous ; molars at their apices flattened, transversely tuberculated ; 

 posterior ones double-fanged ; lips single ; stomach sacculated ; intesti- 

 nal canal of great length ; surface of skin, smooth, oily ; the two 

 cavities of the heart at their lower ends separated from one another, 

 each portion terminating in a distinct point. 



The construction of the bruising molar teeth, the thick hide, and 

 the great length and complicated nature of the intestinal canal, adapted 

 for the digestion of vegetable food, ally these animals to the ordinary 

 pachyderms, and consequently many zoologists have associated them 

 with that group. Other writers have been induced to consider the 

 afBnity to approach nearer to the seals, from the blufi" form of the 

 head, the apical termination of the nostrils, the nictating membrane 

 of the eye ; the lengthened neck, the more perfectly formed hand, and 

 the density of the bones of the skeleton. Again, the peculiar nature 

 of the layer of blubber, which envelops the muscular flesh and is 

 immediately connected by cellular tissue to the external oily, almost 

 naked skin, the entire absence of hinder limbs, the horizontally 

 depressed cartilaginous extremity, the structure of the skeleton in 



* From manatus, provided with hands. 



