5l6 PHILOSOPHICAL TRANSACTIONS. [ANNO 1799. 



cave form, to adapt itself to that of the grinder in the upper jaw. The number 

 of layers does not always correspond with those of the grinder in the upper jaw; 

 but, like them, consists of from 4 to about 13 teeth or laminae. In both jaws, 

 the alveoli are firmly attached, anteriorly and laterally, to the bony plates of which 

 the jaw is composed; but at the posterior part these alveoli are separate from the 

 jaw, and have only a membranous attachment. The alveoli terminate in an apex 

 or point, and become thicker and stronger, as the elephant advances in years. In 

 the lower jaw, the portion of the alveolus which is attached to the inner plate, is 

 thick and spongy; and through the under part of this spongy substance there is a 

 pretty large foramen, for transmitting the blood-vessels and nerves which supply 

 the teeth and lower jaw. The alveolus of the grinder advances in the same manner 

 in the lower as in the upper jaw ; and as the fangs are absorbed it is absorbed also. 

 In proportion as the fangs or roots are added to the grinder, it rises through the 

 alveolus, and cuts the gum ; at the same time the bottom of the alveolus, in which 

 the grinder is formed, becomes more spongy, and shoots up between the fangs, 

 firmly embracing them, and thus preventing the grinder from being shaken or dis- 

 turbed by the trituration of the food. As the grinders of the upper and under 

 jaws wear away, their roots are lengthened, and become more solid, by the internal 

 addition of new matter, till the cavity is entirely filled up. This lengthening of 

 the roots is necessary, to give that portion of the grinder in use sufficient firmness 

 in the jaw, as well as to keep the surface at a proper level above the gum. When 

 the anterior teeth are worn down to the roots, these, with the sockets, begin to be 

 absorbed, to make room for their successors, which are coming forwards. 



The shape of a grinder of the lower jaw is very different from that of one of the 

 upper: in the latter, the grinder advances from behind straight forwards, and the 

 back part has a very convex shape ; whereas the lower grinder advances rather in a 

 bent or curved direction, adapting itself to the shape of the jaw. The surface of 

 this grinder is somewhat of a concave figure, adapted to the form of the corres- 

 ponding grinder in the upper jaw. The upper and lower grinders, and the section 

 of a grinder, show, in the clearest manner, the progress of ossification in the roots, 

 and the manner in which the different teeth are joined. In a young elephant, soon 

 after birth, the milk grinders, with their roots are completely formed ; and even 

 the succeeding or 2d set of grinders have the roots partly added to some of the 

 anterior teeth, which are soon to cut the gum; but the posterior layers are then 

 without roots. Farther back in the jaw, the 3d grinder, which is composed of 

 about 13 teeth, has no appearance of roots; nor have the different teeth any con- 

 nection with each other, except by the common membranes. When these are 

 destroyed, the teeth or rudiments of a succeeding grinder can be easily separated 

 from each other. At this period, the enamel of the third grinder has not been 

 formed, but only the substance of the teeth, which it afterwards covers, adapt- 

 ing itself to the irregularities of the surface. When a grinder is con- 

 siderably worn down, these irregularities of the central lamellae are evident, 



