336 A MEMOIR ON THE EXTINCT 



they present a slight trefoil appearance. The basal ridge, where it exists, is more foveate, 

 less wrinkled, and more prominently tuberculate. Indeed, the true molars of the Peccary 

 have the appearance as if they had been cast of some soft substance, in the same mould 

 as those of the cave head, and had become contracted in bulk and wrinkled in drying. 



The three superior true molars (PI. 37, figs. 5,6,) of the cave head decrease in size from 

 the last to the first; the external lobes are smaller than the internal, and a broad basal ridge 

 surrounds them, open only at the bases internally of the inner lobes, and external part of the 

 base of the antero-external lobe of the last tooth. In the latter, the posterior pair of lobes 

 is shorter than the anterior, and that postero-external is the shortest lobe of those of any 

 of the teeth. . 



The external lobes are simply conoidal ; the inner ones are shaped like those of Hippo- 

 potamus, or expand anteriorly and posteriorly where they come in contact with the for- 

 mer. In the Peccary and Hog, these expansions are more or less isolated, appear- 

 ing as accessory wrinkled tubercles. In the cave head the posterior expansion or fold of 

 the antero-internal lobe comes in contact at its lower part with the anterior of the postero- 

 internal lobe, and thus divides the transverse interlobular fissure. The anterior fold of the 

 former lobe and the posterior of the latter divide the basal ridge anteriorly and posteriorly, 

 and are confluent with it. 



The basal ridge of the superior true molars anteriorly, is thick, delicately folded, and 

 finely denticulate at the free margin. Posteriorly it has nearly the same appearance, 

 except in the last tooth, where it is much thicker, includes two small foveas with wrinkled 

 sides, and is divided by a fissure into two unequal tuberculoid portions. Externally in the 

 last tooth the ridge is continuous round the base of the postero-external lobe to the pos- 

 terior part of the lobe anterior, is thick, folded, and crenulate at margin, and between 

 the lobes includes a fovea containing several minute tubercles. On the other two molars 

 externally the basal ridge is thinnest, and between the lobes includes a fovea with wrinkled 

 sides. Internally in all the upper true molars, constituent folded portions of the basal 

 ridge connect the bases of the inner lobes and enclose foveas with wrinkled sides. 



The inferior true molars (PI. 37, figs. 7, 8.) have a greater antero-posterior diameter 

 than those corresponding above, but are narrower, and their lobes, also in pairs, are 

 more nearly equal and longer. Constituent portions of the basal ridge exist anteriorly, 

 posteriorly, and between the bases of the lobes externally and internally, where it is, how- 

 ever, relatively feebly developed compared with its condition in the upper molars. The 

 teeth also decrease in size from the last to the first. The lobes are elongated, conoidal, 

 those internal sending a fold backward where they come in contact with the external lobes, 

 and the latter sending a like fold forwards. The anterior fold of the postero-external lobe 

 joins the posterior of the antero-internal lobe. The posterior fold of the postero-internal 

 lobe is relatively very slight to the others. 



The basal ridge posteriorly rises into a prominent pyramidal tubercle, most so in the 

 last, where it constitutes the fifth lobe, and least in the first true molar. Between this 

 tubercle and the posterior pair of principal lobes in the last molar, a second and smaller 

 compr< tubercle exists. Anteriorly, the basal ridge- is nearly horizontal and denticu- 



