72 FAUNA ANTIQUA SIVALENSIS. 



mastodon. The crown is very high in front, and declines rapidly 

 behind. In a large specimen of this tooth from ^ssam, the 

 dimensions are upwards of fourteen inches of length by eight 

 inches of height in front, which is reduced to about one-third 

 at the last ridge, while the width does not exceed three inches 

 at the anterior end, from which it narrows gradually behind. 

 The coronal surface is convex across, and also in the antero- 

 posterior direction. There is no indication of the longitu- 

 dinal cleft, which, in the North American and other mas- 

 todons, bisects the crowns of the molars into lateral seg- 

 ments. The ridges, which in the first-mentioned species do 

 not exceed four, are multiplied in the last ujDper grinder of the 

 Indian elephant to twenty-three or twenty-four thin plates, 

 which terminate upwards in slender, cylindrical digitations, 

 hence called Gheirolites by the early palaeontologists, when 

 found separate. The cement substance enters largely into 

 the composition of the tooth, being interstratified with the 

 enamel plates in a layer which also envelopes the entire body 

 of the tooth. The fangs are slender and numerous, bearing 

 a relation to the lamellse, but they are confluent into large 

 hollow groups, which are of inconsiderable length, as the 

 tooth is held firm in the jaw by a large poi'tion of the crown 

 being imbedded in the alveolus. Instead of being protruded _ 

 in a nearly horizontal direction, as in the North American 

 mastodon, the teeth move forwards in the arc of a circle ; the 

 anterior plates in the upper grinders are inclined forwards, 

 and by the process of wear they are ground down, so that the 

 front part of the tooth is trmieated obliquely, as shown in 

 (PL V.fig. 2 (PL I.fig.2, and PL YII. fig. 4, F.A.S.), long before 

 the posterior lamellse come into use. The plane of detrition 

 makes a large angle with the unworn plane of the crown, 

 and in the uj)per grinders it slopes from the inside outwards, 

 being the reverse of what takes place in the mastodons. In the 

 lower jaw the crown of the last molar is concave from behind 

 forwards, and convex across ; the grinding plates, especially 

 towards the posterior end, recline backwards, and the plane 

 of wear, which is concave, slopes from the outside inwards, 

 bearing a reversed relation to that of the upper jaw. The side 

 of the jaw to which the teeth belong is readily distinguished 

 by these characters, and by the circumstance that the upper 

 grinders are convex on the outer, and concave on the inner 

 side, the reverse taking place in the grinders of the lower 

 jaw. The last inferior molar attains a length of fifteen 

 inches, and presents occasionally as many as twenty-six or 

 twenty-seven constituent plates in the largest sized indi- 

 viduals of the Indian elephant. 



When the teeth come into use, the digitated stimmits of 



i 



