DENTAL SYSTEM 13 



the Rhinoceros, the inter-digital glands of the Sheep and many 

 Ruminants, and numerous others. In some of these cases the 

 glands are peculiar to, or more largely developed in, the male ; in 

 others they are found equally developed in both sexes. 



II. DENTAL SYSTEM 



The dental system of mammals may be considered rather 

 more in detail than space permits for some other portions of their 

 structure, not only on account of the important part it plays in the 

 economy of the animals of this class, out also for its interest to 

 zoologists as an aid in the classification and identification of species. 

 Owing to the imperishable nature of their tissues, teeth are 

 preserved for an indefinite time, and in the case of extinct 

 species frequently offer the only indications available from which 

 to derive an idea of the characters, affinities, and habits of the 

 animals to which they once belonged. Hence even their smallest 

 modifications have received great attention from comparative 

 anatomists, and they have formed the subject of many special 

 monographs. 1 



Teeth are present in nearly all mammals, and are applied 

 to various purposes. They are, however, mainly subservient 

 to the function of alimentation, being used either in procuring 

 food, by seizing and killing living prey or gathering and biting 

 off portions of vegetable material, and more indirectly in tearing 

 or cutting through the hard protective coverings of food sub- 

 stances, as the husks and shells of nuts, or in pounding, crushing, 

 or otherwise mechanically dividing the solid materials before 

 swallowing, so as to prepare them for digestion in the stomach. 

 Certain teeth are also in many animals most efficient weapons of 

 offence and defence, and for this purpose alone, quite irrespective 

 of subserviency to the digestive process, are they developed in the 

 male sex of many herbivorous animals, in the females of which 

 they are absent or rudimentary. 



Teeth belong essentially to the tegumentary or dermal system 

 of organs, and, as is well seen in the lower vertebrates, pass by 

 almost insensible gradations into the hardened spines and scutes 

 formed upon the integument covering the outer surface of the 

 body ; but in mammals they are more specialised in structure and 

 limited in locality. In this class they are developed only in the 



1 L. F. E. Rousseau, Anatomic comjiaree du Systeme dentaire chez V Homme el 

 chez les principaux Animaux, 2d ed., 1839 ; F. Cuvier, Des Dents des Mammiferes 

 considere'es comme caracteres zoologiques, 1822-25 ; R. Owen, Odontograimy, 

 1840-45 ; C. G. Giebel, OdontograpMe, 1855 ; C. S. Tomes, Manual of Dental 

 Anatomy, Human and Comparative, 3d ed., 1889. 



