j THE TEETH. 969 
inner or lingual surface in all premolars. The upper are distinguished from the lower bicuspids, 
as pointed out above, by the fact that in the upper the two cusps are separated by a groove, in the 
lower they are united by a ridge ; in the latter also the crowns are more circular (Figs. 646 and 653). 
It will further usually be found that the outer or labial surface of the crown is strongly sloped 
(bevelled) inwards, near the grinding surface, in the lower premolars. The first can usually be 
distinguished from the second by the fact, that, while the lingual cusp and surface are smaller 
than the labial in the first premolar, they are nearly of the same size in the second. In addition, 
the root of the first upper premolar is bifid or nearly so, and its labial ridge is fairly distinct, but 
is indistinct in the second. In the first lower premolar the lingual cusp and surface are very 
small, in fact the cusp is quite rudimentary. It should, however, be added that it is often 
extremely difficult to identify the various bicuspids. The differences may be expressed in 
tabular form thus :— 
Premolars. 
Root. 
Cusp and Surface. 
Upper (have two 
cusps separated - 
| Ist premolar | bifid, or nearly so) Lingual smaller than labial. 
by a groove) PAG Ae single | Lingual nearly as large as labial. | 
| 
Lower (have two | 1st premolar | single | Lingual much smaller than labial. 
cusps united by- - - 
a ridge) | 2nd As G Lingual nearly as large as labial. 
Molar Teeth (dentes molares)—The molar teeth, also known as the grinders or 
multicuspidati, are twelve in number—three on each side above and below—and 
are distinguished as first, second, and third molars. The latter is also known as 
the wisdom tooth, owing to its late eruption. All the molars are characterised by 
the large size of the crown and the possession of three or more trihedral cusps on 
the masticating surface (Figs. 652 and 653). They are the largest of all the teeth, 
but they diminish in size from the first to the third, the last being, as a rule, 
the smallest of the three. In shape the crown is more or less quadrangular, 
with convex labial and lingual surfaces. The roots are either two or three 
in number, but frequently in the wisdom teeth they are united to a varying 
degree. 
The molars of the upper and lower jaws differ so considerably in their further 
details that they must be considered separately. They may be most readily dis- 
tinguished from one another by the fact that normally the upper molars possess 
three roots (Figs. 650 and 651), whilst the lower molars have two at most. The 
number of cusps, though not so reliable a guide as the form of the root, is also 
generally sufficient to distinguish them. In the upper molars there are either 
three or four cusps, whilst in the lower the number is most commonly five (see, 
however, page 971). 
In the upper molars, the crown, viewed from the grinding surface (Fig. 652), is 
rhomboidal in shape (7.e. quadrangular with the angles not right angles). The outer 
(labial) and the inner (lingual) surfaces are convex. The number of cusps is either 
four or three. On the first there are invariably four—two on the labial and two 
on the lingual side—the antero-internal (proximo-lingual) of these being connected 
with the postero-external (labio-distal) by an oblique ridge (Fig. 652), which is 
also found on the second and third molars when these bear four distinct cusps. 
The second upper molar has either four or three cusps in about an equal proportion 
of European skulls, whilst in the third the number is much more frequently three 
than four. The roots in the upper molars are three in number (except, occasionally, 
when the three roots of the wisdom tooth are confluent), two being external or 
labial, and the third internal or palatal (Figs. 650, 651, and 654). 
In the lower molars the crown, viewed from above (Fig. 655), is somewhat 
eubical. The outer and inner surfaces are convex, as in the upper molars. The 
jirvst, as a rule, bears five cusps, two being on the outer side, two on the inner, and 
the fifth behind and external, that is, between the two posterior cusps and somewhat 
to the outer side. The second has usually only four cusps; a fifth, however, is 
sometimes present. The ¢hird has either four or five, the former number more 
frequently than the latter. ° 
The roots of the lower molars are two in number, each wide, grooved, and 
