110 
TEliTIART VEllTEBKATA OF THE FATtM. 
llio middle into a longitudinal ridge, such that when the tooth is worn the resulting 
wear-surfane of the main cusp is continued back on this median elevation of the talon. 
'I'he next tooth 3) is larger and especially wider; it also consists of a high 
anterior ])ortion and a posterior talon. The anterior part is composed of tliree cusps, 
one of which forms the antero-internal angle of the tooth, Avhile behind this the 
other two imperfectly separated cusps form a transverse ridge. In wear, the abraded 
surface of the antero-internal cusp is continuous with that of the outer one of the 
transverse pair, and this again unites with the surface of the talon, which has a ridge 
towards its outer side, rising into a tubercle posteriorly. 
The last premolar [pm. 4) is wider, and its anterior cusp is less distinctly developed 
than in pm. 3. On the other hand, the inner cusp of the transverse pair is much 
larger and more prominent. The talon also bears a more distinct postero-external 
cusp. In the third and fourth premolars the cingulum is slightly developed on the 
outer and posterior sides ; on the latter it forms the raised edge of the talon. 
The first molar (PI. IX. fig. 2, m. 1) consists essentially of a pair of transverse ridges, 
each composed of a pair of tubercles and a small talon. The inner tubercles are 
somewhat higher and sharper than the outer, which are the most worn. There 
is a tendency to form small tubercles in the valley between the two main ridges, 
connecting the inner ends of the outer tubercles. The talon consists of a blunt 
tubercle nearly in the middle line, and a smaller, often obscure, ensp on the inner 
side. In the third molar [m. 3) the talon is much larger, the main cusp being larger 
and tending to become subdivided into two, while the inner cusp also is prominent, 
so that in this tooth the talon forms a third transverse ridge. This third molar 
is extremely similar to the corresponding tooth in some mandibles of Palceomastodon, 
while m. 1 and m. 2 differ considerably, owing to the small development of the third 
lobe ; but at the same time the differences are merely of degree and not of structure. 
The cingulum is well developed on the outer side of the lower molars. 
Of the milk-dentition only the last lower milk-molar is known. This is well shown 
in a portion of the right ramus of a young mandible (text-fig. 43), in which 
mm. 4 and m. 1 are well preserved, and beneath the former the crown of 4 is 
present. Mm. 4 is much like the permanent molars ; it is bilophodont with a small 
talon forming the rudiment of a third ridge. 
Vertehral Column. — The vertebral column of Moeritherium is fairly completely 
known. In several cases vertebrae have been discovered associated with portions of 
skulls and teeth that can be definitely determined as belonging to M. lyonsi ; and in 
addition to these an almost complete vertebral column has been found associated with 
a very imperfect skull which is undoubtedly that of a species of Mairltheriuni^ though 
whether of M. lyond or not is uncertain. The vertebrae known to belong to M. lyonsi 
will be described first. 
In the atlas (PI. XI. fig. 1) the deep cups for the occij)ital condyles [cond.) in correlation 
