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. 
Il, 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, but 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.! 
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 
1L. F. E. Rousseau, Anatomie comparée du Systeme dentaire chez ? Homme et 
chez les principaux Animaux, 2d ed., 1839; F. Cuvier, Des Dents des Mammiferes 
considérées comme caractéres zoologiques, 1822-25; R. Owen, Odontography, 
1840-45 ; C. G. Giebel, Odontographic, 1855; C. S. Tomes, Manual of Dental 
Anatomy, Human and Comparative, 3d ed., 1889. 
