PROFESSOR OWEN ON SOME SPECIES OF THE EXTINCT GENUS NESODON. 295 
the postero-external angle of the crown is slightly produced ; the increase in the size 
of the crown is chiefly in its antero-posterior extent and length, which latter is 
7^ lines before it divides into fangs, two of which are external, short and divergent. 
The total length of this tooth is 10 lines. 
The fourth grinder (ib. d*), presents an increase of size in the same directions as 
the third was enlarged, but to a minor degree in antero-posterior extent than in 
length, in proportion to which the crown is narrow transversely at its grinding sur- 
face. The posterior external longitudinal eminence has much subsided, and has lost 
all the character of a ridge ; the anterior external longitudinal ridge continues to be 
angular and well-marked ; it is near the similarly produced ridge-like anterior angle 
of the crown, which projects outwards, in advance of the hind part of the third 
grinder. The bifurcating internal enamel- fold penetrates the anterior half of the 
grinding surface ; a second wide simple fold, parallel with the first, answers, in this less 
worn tooth, to the enamel island in the third grinder ; the postero-external angle is 
more produced than in that tooth. The length of the crown is 1 inch, following its 
curvature, which is now well-marked, and one-half of the crown penetrates the sub- 
stance of the maxillary, contracting before it divides into fangs, two of which are 
external, short and divergent; the entire length of the tooth is 1 inch 5 lines. 
The crown of the fifth molar (ib. m i) had but recently begun to protrude from its 
socket, and is only abraded at the anterior half of the grinding surface. The branches 
of the forked enamel-fold appear as two distinct folds, and there is a slight depression 
behind the beginning of the main fold. In the hinder lobe of the tooth there is a 
wide fold on the inner side, and a depression at its end, which would give rise to an 
island of enamel at a certain stage of abrasion of the crown. The thickness of the 
exposed and worn surface of this grinder does not exceed that of the preceding tooth ; 
the breadth or antero-posterior extent is a little greater; but the length of the crown, 
which is imbedded in the jaw-bone, is considerably greater; it measures, following 
the outer convexity, 1 inch 8 lines, increasing in thickness, and slightly diminishing 
in breadth, and terminating in a wide pulp-cavity, without trace of fangs. The ridge- 
like anterior angle is produced external to, and in advance of, the fourth grinder, in 
the same imbricated manner as the fourth overlaps the third grinder, and this the 
second. 
In the lower jaw the only incisor remaining (Plate XVI. fig. 6, i a) is that answering 
to the third in the upper jaw; but it is double the size of that tooth ; the crown has 
the usual trenchant incisive form convex externally, slightly concave on the opposite 
surface, with a long, straight fang, contracting as it sinks in the socket. 
The canine (ib. c) is somewhat less, with the crown similarly compressed, but with 
its worn margin more angular than in i a. 
The first molar (ib. d i) much resembles the canine, but is somewhat larger, and 
the longitudinal convexity and depressions of its inner surface are more marked ; its 
root is single and contracted like that of the canine. 
