DENTAL SYSTEM 29 



trenchant, and piercing, and are situated wide apart, so as to give 

 the firmest hold when fixed in the victim's body. The jaws are as 

 short as is consistent with the free action of the canines, so that no 

 power may be lost. The incisors are very small, so as not to 

 interfere with the penetrating action of the canines, and the 

 crowns of the molar series are reduced to scissor-like blades, with 

 which to pare oft' the soft tissues from the large bones, or to divide 

 into small pieces the less dense portions of the bones for the sake of 

 nutriment afforded by the blood and marrow they contain. The 

 gradual modification between this and the two following types will 

 be noticed in their appropriate places. 



In the most typical insectivorous animals, as the Hedgehogs 

 and Shrews, the central incisors are elongated, pointed, and project 

 forwards, those of the upper and lower jaw meeting like the blades 

 of a pair of forceps, so as readily to secure small active prey, quick 

 to elude capture, but powerless to resist when once seized. The 

 crowns of the molars are covered with numerous sharp edges and 

 points, which, working against each other, rapidly cut up the hard- 

 cased insects into little pieces fit for swallowing and digestion. 



The omnivorous type, especially that adapted for the con- 

 sumption of soft vegetable substances, such as fruits of various 

 kinds, may be exemplified in the dentition of Man, of most 

 Monkeys, and of the less modified Pigs. The incisors are moderate, 

 subequal, and cutting. If the canines are enlarged, it is usually 

 for other purposes than those connected with food, and only in the 

 male sex. The molars have their crowns broad, flattened, and 

 elevated into rounded tubercles. The name Bunodont, or hillock- 

 toothed, has been proposed for molars of this type, and will 

 frequently be found convenient. 



In the most typically herbivorous forms of dentition, as seen in the 

 Horse and Kangaroo, the incisors are well developed, trenchant, and 

 adapted for cutting off the herbage on which the animals feed ; the 

 canines are rudimentary or suppressed ; the molars are large, with 

 broad crowns, which in the simplest forms have strong transverse 

 ridges, but may become variously complicated in the higher degrees 

 of modification which this type of tooth assumes. 



Various forms of teeth of this type will be noticed among the 

 Ungulates and Rodents. 



The natural groups of mammals, or those which in our present 

 state of knowledge we have reason to believe are truly related to 

 each other, may each contain examples of more than one of these 

 modifications. Thus the Primates have both omnivorous and 

 insectivorous forms. The Carnivora show piscivorous, carnivorous, 

 insectivorous, and omnivorous modifications of their common type 

 of dentition. The Ungulata and the Rodentia have among them 

 the omnivorous and various modifications, both simple and complex, 



