COMPARATIVE ANATOMY OP THE TEETH. 289 



acter is the constancy of eight incisors in the lower jaw, 

 the two outer of which Mr. Owen calls canine. The usual 

 dental formula gives 32 teeth to the ruminantia: 6 bi- 

 cuspids and 6 molars to the upper jaw; to the lower, 6 

 incisors, 2 canines, 6 bicuspids, and 6 molars. A wide 

 space separates the incisors and bicuspids. 



The upper bicuspids have three roots; the upper true 

 molars have four roots. In the lower jaw both bicuspids 

 and molars have but two roots; but the second root in the 

 last molar consists of two connate roots. 



CETACEA. This order of mammalia includes the whales, 

 which have no teeth,* properly speaking, but horny sub- 

 stitutes, called "whale-bone" or "baleen." The so-called 

 teeth of the right whale are in the form of plates, termin- 

 ating in a fringe of bristles. In a new-born whale Mr. 

 Owen found the number of these plates to be 190. The 

 largest are arranged on each side of the upper jaw in a 

 longitudinal series and close to each other, vertically, with 

 their flat surfaces looking forwards and backwards, and 

 their free margins outwards and inwards. The smaller 

 plates are disposed in an oblique series within the larger. 

 The base of each plate is described as being fixed upon a 

 pulp developed within a broad, shallow depression of the 

 gunr, and covering the entire surface of the maxillary and 

 anterior portion of the palate bones the whale thus hav- 

 ing palatal teeth. The base of each plate is hollow, for 

 receiving the pulp bearing the same relation to it that 

 the pulp of a true tooth does to its cavity. 



THE SECOND CLASS OF ANIMALS, BIRDS (AVES.) 



As the organs of prehension of this class consist of a horny 

 substance, and are therefore not teeth properly speaking, a 

 remark or two is all that is considered necessary to be made 

 in reference to these substitutes or mere representatives of 

 teeth. 



It is true, as has been remarked, that strictly speaking, 



* Some varieties in this order, it is thought, have teeth proper. 



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