ORGANS OF TOUCH DIGESTIVE SYSTEM. 35 



tend anteriorly over the Stenoriian canals, to the posterior border of 

 the vorner. The Carnivora and Rodentia have in part only the Ste- 

 nonian canals, while even these are wanting in the Horse. 



Organs of Touch. 



The tips of the fingers are alone specially constructed as organs 

 of touch in Man ; still, many Apes, as Cebus Azarae, possess a fine 

 tactile sense in these parts. In the rest of the Mammalia, the up- 

 per lip, the nose, and snout, especially the bristles or vibrissoe seat- 

 ed upon the upper lip and at the angles of the mouth, the follicles of 

 which often receive very large twigs from the infra-orbital branch 

 of the fifth pair, serve chiefly as organs of touch. In the common 

 Otter the vibrissae of the angle of the mouth receive twigs from the 

 alveolar branch of the third division of the fifth pair, and in the 

 Seals, the numerous ramifications of the infra-orbital form an 

 areolar plexus, before they enter the follices of the hairs of the 

 beard. 



DIGESTIVE SYSTEM. 



THE organs of mastication, namely, the Teeth, present in the Mam- 

 malia remarkable diiferences in number, form, and structure, which 

 stand in such close relation with the whole economy, mode of life 

 and form of the animal, that its place in the system can, as a rule, 

 be determined from a few fragments of the teeth. In some genera 

 of the lowest orders, e. g. Manis, Myrmecophaga, and Echidna, 

 the teeth are completely wanting. In others, as in the Whales, 

 their place is occupied by mere horny laminae, called whale-bone. 

 /The teeth occur invariably only in the intermaxillary upper and 

 lower jaw-bones, and are generally implanted in sockets. As a rule, 

 there are two sets of teeth, which succeed each other, the milk teeth 

 and the permanent teeth, and these, as in Man, are divided into 

 molar, canine, and incisor teeth, the first of these being the most uni- 

 versally present. Three kinds of teeth may be distinguished, 1st, 

 Simple teeth, denies simplices, in which the crown, as in man, is sim- 

 ply covered over with enamel. This is the case in the higher orders, 

 the Apes, the Cheiroptera, Carnivora, Marsupiata, and many Ro- 

 dentia, viz., the Mice, Marmots, &c. 2d, Enamel-folded teeth, 

 denies complicati, where the enamel is inflected into the dental sub- 

 stance, a form met with in many Rodentia, as Myoxus, Castor, and 



