24 
TEllTIAliT VERTEBRATA OF TEE FAYCtM. 
(see text-fig. 0, p. 18) ; at the same time the difference is less than that between the 
upper ))rem()lars and molars. They are four in number, the three posterior ones 
being double-rooted. Fm. 1 is not known in A. zitteli, but in A. andrewsi its 
crown is very like the others ; in both species it has a single root. 
Each })remolar consists of two columns separated externally by a deep vertical 
groove. In early stages of wear the pattern is a double V, but later the concavity of 
the V’s becomes obliterated, and the inner face of the teeth is nearly straight. In 
some unworn specimens the postero-internal end of the anterior V is seen to 
project somewhat across the opening of the posterior V so as partially to close it : 
this projection seems to correspond with the metastylid of some other ungulate teeth 
(e. g. llyrax \_Procavia^^, Equus). The cingulum is well developed on the inner 
face of the teeth, and is also present in some specimens, though not all, on the 
outer side between the main columns. 
The closely crowded canines and incisors are, so far as known, closely similar 
to one another. 'I'hey are high columnar teeth, convex outwards from above 
downwards, and nearly rectangular in section. The outer face of the crown is 
strongly convex from side to side ; on the inner side the cingulum is well developed, 
and between it and the inner face of the tooth there is a deep, more or less 
developed pit or “ fosette.” 
The lower milk-dentition is imperfectly known, and in such specimens as are 
preserved it appears that the milk-molars are practically identical in form with 
the molars of the permanent series. 
Vertebral Column. — In correlation with the great size and weight of the skull the 
atlas (text-fig. 8) is very large and massively constructed, its width being especially 
great. The condylar cups {cond.) are large and widely separated botli above and 
below ; they are strongly concave from above downwards, and are much wider above 
than below, where they narrow rapidly as they pass on to the ventral bar. The lateral 
surfaces for the axis {ax.) consist of a subcircular, slightly concave upper portion, from 
the outer and lower side of which a less well-defined triangular area runs down 
to the ventral bar, nearly reaching the outer border of the odontoid face [od.]. 
This is very broad, sharply defined, slightly concave from side to side, and prolonged 
somewhat backwards on a median prominence of the ventral bar, the posterior 
angle of which forms a blunt hypapophysis. 
The neural arch is wide both from side to side and from beh)re backwards ; 
its upper suiface is strongly convex from before backwards and forms a slight 
prominence on either side of the middle line (/zs.). Laterally, close to its anterior 
border, the arch is perforated by the narrow slit-like passage which transmits the 
first spinal nerve {sp-f.). This foramen opens into a groove, the ])Ostcrior border 
of which forms the anterior edge of the large transverse process {t.p.). This is very 
