OCR Text |
Show 1869.] MR. G. BUSK ON FOSSIL REMAINS FROM BORNEO. 411 posterior vallum, which extends across from the posterior and external angle of the tooth to the side of the posterior column. This vallum. is in some species deeply emarginate in the middle, and in others presents in the middle a denticle or small pointed cusp. On the inner face are seen the two pyramidal columns separated bv the entrance of the median valley or sinus; and at the bottom of this entrance there is frequently a small tubercle, the median tubercle. Within the median sinus is seen projecting into it from the posterior column a process of enamel, which is usually termed the " crochet," and by some the " posterior combing-plate;" and in addition to this, in many cases, there are one or more small projections of the same kind, usually springing from the outer lamina into the sinus, which have been termed the "anterior combing-plate or plates." They might be conveniently designated as the crista or cristce. To describe the Sarawak teeth in the same order:- 1. On the dorsum the anterior costa (a c, fig. 1) is very prominent and prolonged to the base ot the crown in its present immature condition. It is of considerable thickness. The second or median costa is very distinct aud rounded ; the third or posterior almost obsolete, Fig.l. Dorsum of m. 2, Sarawak tooth. being visible only towards the base and quite at the apex. The hinder border of the dorsum is much raised, so that between it and the anterior costa the surface of the tooth is deeply hollowed or concave. 2. The anterior vallum (a, v. fig. 2, p. 412) is strongly developed, and the anterior sinus deep, especially at the base. 3. The posterior vallum (p. v. fig. 3, p. 412) is deeply emarginate and presents no trace of a denticle, and its upper edge is even and not tuberculated. 4. On the inner face the entrance of the median sinus is contracted at the bottom and wide upwards, so that the columns, and especially |