A DUCK-BILLED MAMMAL. 247 



ODONTOG'RAPHY. A description of the teeth. 



ODON'TOID. Tooth-shaped. 



ODONTOT/ITHOS. A sort of incrustation, of a yellowish color, 

 which forms at the coronse of the teeth, and is called ' tartar.' 

 It consists of 79 parts of phosphate of iime, 12| of mucus, 1 

 of a particular salivary matter, and 7| of animal substance, 

 soluble in chlorohydric acid. A species of infusoria, ' dentic- 

 ola hominis,' has been found in it. 



ODONTOL'OGY. An anatomical treatise of the teeth. 



ORAL. Relating to the mouth or to speech. 



ORAL EPITHE'LIUM. See 'Epithelium/ 



ORNITHORHYN'CHUS. An effodient (digging), monotrematous 

 mammal, with a horny beak resembling that of a duck, and 

 two merely fibrous cheek teeth on each side of both jaw,s, not 

 fixed in any bone, but only in the gum ; with pentadactylous 

 (five-fingered) paws, webbed like the feet of a bird, and 

 formed for swimming, and with a spur in the hinder feet, 

 emitting a poisonous liquid from a reservoir in the sole of the 

 foot, supplied by a gland situated above the pelvis, and by 

 the side of the spine. The animal is covered with a brown 

 fur. It is found only in New Holland, and is sometimes 

 called Water Mole. Bell. 



As the name of the order imports, the alimentary, urinary, 

 and reproductive organs open into a common cloaca, as in 

 birds ; mammary glands are present, secreting milk for the 

 young, which are born blind and naked ; there are no prom- 

 inent nipples, and the mammary openings are contained in 

 slits in the integument ; M. Verreaux says the young, when 

 they are able to swim, suck in the milk from the surface of 

 the water, into which it is emitted. American Cyc. 



'Duck-Bill,' the English name of the Ornithorhynchus par- 

 adoxus, found in Van Diemen's land and Australia. In its 

 bill-like jaws, its spurs, its monotrematous character, its non- 

 placental development, and its anatomy, it appears to be a 

 connecting link between birds and mammals. The Duck-Bill 

 is the only animal of its genus. It is about fifteen inches 

 long ; it climbs trees with facility, and digs burrows, often 

 thirty feet long, in the river bank, with one opening above 

 and another below water. It inhabits ponds and quiet 

 Streams, swimming about with its head somewhat elevated, 



