144 
TERTIAliT VERTEBRATA OF THE FAYtjM. 
found in the immediate neighbourliood of the type mandible of P. headnelli, and 
from their size probably referable to that species. Other specimens differing only 
in their smaller dimensions will he found mentioned in the Catalogue, where they 
are referred provisionally to other species. 
'fhe ailas of P. headnelli (PI. XV. fig. 3) is of very large size, equalling the same 
\ ertebra in a small Indian Elephant. The condylar cups (cond.) for the occipital condyles 
are deep ; they are wide dorsally, hut narrow considerably towards their lower end. The 
articular surface for the skull is rather wider and lower than in Mastodon or Elephas, in 
which the long axis of the condylar cups is nearly vertical. The arch forms a low nearly 
straight bar, which bears on its dorsal surface a median transverse ridge {n.sp.) separating 
an anterior rugose surface for the attachment of muscles from a nearly smooth posterior 
one. Anteriorly the base of the arch is perforated by a foramen for the transmission of 
the first spinal nerve. In Elephas and Mastodon the arch is more elevated and shorter 
from side to side. The ventral bar is likewise longer and straighter than in those genera, 
though some species of Mastodon (e. g., M. americanus) approach the present form 
in this respect. The notch for the odontoid process (o^k) is broader and shallower than 
\\\ Mastodon., Elephas primi genius, and P. maximus, in which it is comparatively narrow 
and deep ; E. africanus resembles Ealceomastodon most nearly in this respect. The 
distinct separation of the odontoid notch from the neural canal distinguishes the atlas 
in this genus from that of Arsinoitheriimi. The posterior surface for union with the 
axis differs widely from the form seen in the atlas of other Proboscidea. In these 
the lateral surfaces for articulation with the centrum of the axis are continuous both 
with that for the lower surface of the short blunt odontoid process and with one 
another beneath it. In PaUeoinustodon, on the other hand, the two lateral surfaces, 
which make only a small angle with the transverse plane, are distinct from one 
another and are not continuous with the odontoid facet, which is a cylindrical surface 
on the upper face of the ventral bar ; this latter bears on its postero-ventral border 
a blunt hypaj)opbysial process. The transverse processes {tp.) are about the same 
size as in the Indian Elephant ; they are ])erforated at their base by a foramen (t’.c.) 
which is much smaller than that found in the atlas of Mastodon and Elephas. The 
upper pedicle of the transverse process is much wider than the ventral one ; the 
anterior face of the transverse ])rocess looks downwards and forwards. On the whole, 
this vertebra approaches very nearly to the atlas of the Elephant, differing from it 
mainly in (I) the form and relations of the surfaces for articulation with the axis ; 
(2) the smaller size of the vertebrarterial canal ; (3) the more oval oiitline of the 
surface for articulation with the skull. 
The axis (PI. XVI. figs. I, I a) differs much more widely from the modern Pro- 
l)Oscidean type than does the atlas, and at the same time ap]U’oximates more nearly to 
the form seen in some Ungulates (e. g., Jlippopotanins) with necks of moderate length. 
The odontoid process (od.) is large and somewhat comj)ressed laterally ; its ventral 
