26 MR. A. L. ADAMS ON THE OSTEOLOGY OF 
severe pressure on the enamel of the last ridge, at the same time it seems pretty 
generally the case that the succeeding tooth does not commence to attrite the pre- 
decessor until the latter has about one third of the crown worn out. Again, the 
crown does not graduate, like last teeth, towards the posterior talon; moreover the 
heel is only about 2°5 inches behind the anterior margin of the coronoid, and the plates 
(see fig. 10a) are arcuated as in teeth that are being pushed onwards. These facts 
dispose me to regard the above as being penultimate true molars. 
The discal pattern displays the expansions and excentral angulations of a well-bent 
lower molar. ° The enamel is in no wise thick ; and there is scarcely a trace of crimping. 
The crown, as obtains in certain last lower molars, is broad in front and narrow 
posteriorly. 
2. The almost worn-out fragment of an upper molar No. 50 (Pl. II. fig. 7) contains 
seven and a half ridges in 2°8 inches, and, from dimensions and consistence of enamel 
and discal pattern, might have belonged to this series, the crowding and parallelism of 
the plates being, as previously shown, a result of the advanced stage of wear. 
C Series.—1. The upper molar No. 38 (Pl. IL. fig. 1) represents a broader crown 
than ordinarily obtains, from the circumstance that the plane of attrition is oblique 
instead of horizontal. As to its claims to the position of second true molar I 
think there cannot be much doubt. ‘There is a broad pressure-scar on the posterior 
aspect. The double anterior fangs have been broken off close to the crown, and 
support only the first ridge, which is worn to the common base; therefore, allowing for 
the loss of one plate and the anterior talon, we are seemingly justified in concluding that 
the original formula amounted to at least twelve ridges. There are ten ridges in a space 
of 5:4 inches, which with those worn out would make up the length to fully 6:5 inches. 
The well-worn and perfect condition of the disks shows the decided pattern of the 
largest form as displayed in the well-attrited crowns of its preceding teeth. The 
contrast between the above and PI. II. fig. 7 is remarkable. Although the latter is 
almost worn out, it displays seven disks in a space of 3 inches, which is precisely the 
dimensions of another fragment of a similar tooth in germ (see No. 69 of the collection). 
2. Another well-worn fragment of an upper tooth of the same type as No. 38 is shown 
in No. 80 (Pl. VIII. fig. 4). It contains six ridges in a space of 3:5 inches, which 
would make the original dimensions about the same as No. 38. Here the shallow disk, 
with the faint crimping on the cement-side of the macherides, and some arcuations of 
the plate with the pronounced angulations are well seen; whilst a vertical section of 
the opposite tooth of the same individual displays the thick intervening cement as com- 
pared with the breadth of the plates. 
3. But a far more convincing proof of teeth analogous to the above being penulti- 
mate true molars is seen in Pl. VIII. fig. 2, where the last of the series is in situ, with 
a fragment («) of the penultimate also in place. ‘The latter holds six ridges in a space 
of 3°3 inches. 
