532 
ORIGINAL ARTICLES. 
groove # (I) more or less deep and inclined forwards into two equal 
or subequal arese, of whicli the anterior is tbe higher. The posterior 
(N) is more or less rounded off, without costse, As in the upper 
molar series the premolars may be differentiated from the true molars 
by the median groove traversing the base in the latter, and never in 
the former. The inner aspect is divided by the two Y-shaped open 
valleys, of which the anterior (A) is smaller and shallower than the 
posterior (B), into three colles. Of these the anterior (D) is the 
smaller, the median (E) the larger. In the premolar series the latter is 
generally more tumid than the rest. The two ‘lobes’ of the tooth, are 
composed, the anterior of the median and anterior colles, the posterior, 
of the posterior collis (F). The summit of the unworn anterior lobe is 
broadly and deeply, that of the po sterior more faintly notched. The an¬ 
terior aspect is flattened except in Pm 2, and traversed by a small ridge 
or guard, springing from the first costa and reaching inwards. It is 
found generally at a distance of two-thirds of the whole length of crown 
from the base, and is very strongly developed in the true molars. The 
posterior aspect rounded except in M 3, is also traversed by a small 
upward tending guard, generally arched, but sometimes straight. 
Springing from the outer side it dies away without impinging upon 
the inner surface of the third collis. 
The fangs are four, divaricate connate, the outer with its fellow 
of the inner side. The tips of those of m 1 and 2 are slightly twisted, 
the anterior pair dextrally, the posterior sinistrally. Among the 
anomalies is the presence of a cusp at the entrance of the Pos¬ 
terior valley in M 1, 2, 3, at the posterior side of the same valley in 
M 1, and at the anterior side in Pm 3. The ‘ Crochet’ on the an¬ 
terior border of the Posterior valley which M. Christolfi mentions 
may be cited also as an accidental variety. A cingulum also is found 
on the inner and outer surfaces of M 1 and 2. 
1. Pm 2. In Pm 2 (fig. 7), the first of the Premolar series, the 
median groove (I) is very shallow and oblique, and, if prolonged, would 
cut the middle of the exterior and posterior fang. The anterior (M) 
is twice as large as the triangular posterior area (N), and is traversed 
by a faint diagonal depression, which separates the two almost obso¬ 
lete costae. The exterior base is tumid. The anterior valley (A) is 
shallow, open, and Y-shaped, the posterior (B), very narrow and 
deep, is constricted by the great posterior extension of the median 
collis, which here reaches its relative maximum of development. The 
anterior collis is small, and the ascending ridge which sweeps round 
the anterior valley presents a trenchant edge. 
Inch. 
Maximum height of anterior area.1*3 
„ „ posterior area.1*06 
* Fig. 5, 6, show the plan upon which the permanent lower molars are formed, 
f Ann. des Sciences, Vol. iv. 1835. 
