The grinding teeth of the elephant pro gressively increase in size, and in the number of lamellar divisions, from the first to the last ; and, as the rate of increase in both respects is nearly identical in both jaws, I shall describe them chiefly as they appear in the lower one.
The first molar, which cuts the gum in the course of the second week after birth, has a sub-compressed crown, nine lines in autero posterior diameter, divided by three trans verse clefts into four plates, the third being the broadest, and the tooth here measuring six lines across t ; the first and second plates have two mammilloid summits ; the third and fourth have three or four such; there is a sin gle and sometimes a double mammilloid sum mit at the fore and back part of the crown : the base slightly contracts, and forms a neck as long as the enamelled crown, but of less breadth, and this divides into two, an anterior and posterior, long, sub-cylindrical, diverging, but mutually incurved fangs ; the total length of this tooth is one inch and a half. The corresponding upper molar, which Mr. Corse describes as cutting the gum a little earlier than the lower one, has the anterior single digital process or mammilla, and the pos terior talon developed into a fifth plate, smaller than the fourth, with which its middle part is confluent ; the neck of this tooth is shorter, and the two fangs are shorter, larger, and more compressed than those of the lower first molar. This tooth is the homologue of the probably deciduous molar (d. 2) in other Ungulates ; it is not a mere miniature of the great molars of the mature animal, but re tains, agreeably with the period of life at which it is developed, a character much more nearly approaching that of the ordinary Pa chydermal molar, manifesting the adherence to the more general type by the minor com plexity of the crown, and by the form and relative size of the fangs. In the transverse divisions of the crown we perceive the affinity to the Tapiroid type, the different links con necting which with the typical elephants are supplied by the extinct Lophiodons, Dino theriums, and Mastodons. The sub-division of the summits of the primary plates recalls the character of the molars, especially the smaller ones, of the Phacochere in the Hog tribe. As the elephant advances in age the molars rapidly acquire their more special and complex character.
. The first molars are completely in place, and in full use at three months, and are shed when the elephant is about two years old.
The sudden increase and rapid develop ment of the second molar may account for the non-exigence of any vertical successor to the former tooth, or "premolar," in the elephant. The eight or nine plates of the crown are formed in the closed alveolus, behind the first molar by the time this cuts the gum, and they are united with the body- of the tooth, and most of them in use, when the first molar is shed.
The average length of the second molar is two inches and a half; ranging from two inches to two inches and nine lines. The greatest breadth, which is behind the middle of the tooth, is from one inch to one inch three lines. There are two roots : the cavity of the small anterior one expands in the crown, and is continued into that of the three anterior plates. The thicker root supports the rest of the tooth. The second molar is worn out and shed before the beginning of the sixth year.
The third molar has the crown divided into from eleven to thirteen plates ; it averages four inches in length, and two inches in breadth, and has a small anterior, and a very large posterior root ; it begins to appear above the gum about the end of the second year, is in its most complete state and _exten sive use during the fifth year, and is worn out and shed in the ninth year. The last rem nant of the third molar is shown at m. 3, fig. 592.
It is probable that the three teeth above de scribed arc homologous with the deciduous mo lars, d.2, d. 3, and d. 4, in the Hyrax and horse.
The fourth molar presents a marked supe riority of size over the third, and a somewhat different form : the anterior angle is more obliquely abraded, giving a pentagonal figure to thd tooth in the upper jaw (fig. 592. m. The number of plates in the crown of this tooth is fifteen or sixteen : its length between seven and eight inches ; its breadth three inches. It has an anterior simple and slender root supporting the three first plates ; a second of larger size and bifid, supporting the four next plates ; and a large contracting base for the remainder. The fore-part of the grinding surface of this tooth begins to pro trude through the gum at the sixth year : the tooth is worn away, and its last remnant shed, about the twentieth or twenty-fifth year. It may be regarded as the homologue of the first true molar of ordinary Pachyderms (m. 1).