PAL.EOMASTODON. 
145 
border is in the same line witli the hypapophysial ridge on the centrum : on its 
lower surface it bears an oval facet for articulation with the ventral bar of the atlas, 
this facet being sharply defined and separated from the lateral articular surfaces, which 
arc oval in outline and make an angle of aboiit 115° witli the long axis of the odontoid 
process. The centrum is very long compared with that of the later Proboscidean axis ; 
it bears a median hypa])ophysial ridge, which deepens posteriorly in such a way that 
the posterior articular surface is greatly deepened ventrally. There are small transverse 
processes [t.]).) perforated at their base by a large vertebrarterial foramen. The neural 
arch is very high, but the precise outline of the spine [n.sp.) cannot be determined, 
owing to the imperfection of the specimens ; it can be seen, however, that it was high 
and broad, and overhung the arch both before and behind. A smaller axis vertebra, in 
which the neural spine is nearly complete, shows that it consisted of two plates meeting- 
in front at an acute angle and enclosing posteriorly a deep fossa for the insertion of 
muscles or ligaments. This axis differs from the ordinary Proboscidean type in the 
following points: — (1) the large size of the odontoid process, which in the later forms 
is reduced to a mere knob with its articular surface continuous with that of the 
centrum which extends beneath it ; (2) the much greater length of the centrum ; 
(3) the less massive, but much higher, neural spine. On the other hand, it is 
very similar to that of Mceritherium. The neck in Palceomastodon was probably 
considerably longer and more mobile than in the later Proboscidea. 
Fore Lwih. — An incomplete left scapula collected in the same locality as the type 
mandible is the only evidence of that bone yet discovered. It is very closely similar 
to the scapula of Elephas, differing only in the rather slighter prominence of the 
coracoid process and in Avidening out less rapidly posteriorly above the glenoid cavity, 
the whole blade being probably rather less expanded above than in Eleplms. The 
glenoid cavity is an elongated oval, the prescapular fossa is extremely narroAv, and 
the process projecting backwards from the middle of the spine in Elephas here seems 
to be situated a little nearer the glenoid end. 
In the case of the humerus (PI. XVI. figs. 2, 2 a) also the only specimen that 
can be definitely determined as belonging to Palceomastodon beadnelli, was collected 
near the type mandible. In its general character this bone is like that of the later 
Proboscideans, but is somewhat stouter and broader in proportion to its length, and 
approaches more nearly some specimens of the humerus of Mastodon Avith Avhich 
it has been compared. It is also very similar to the humerus figured by de Blainville 
(‘ Osteographie,’ Atlas, vol. v. pi. xiii., Elephas) as that of Tetrahelodon angustidens. 
The deltoid crest [d.) is greatly developed and strongly bent over to the outer side 
of the bone. The very prominent and Avell-marked supinator ridge {sp.r.) is shorter 
than in the Elephants, though still very large ; its flat outer surface is slightly 
inclined to the long axis of the shaft. The inner trochlea is much larger than the 
outer, and, in fact, seems to be larger proportionately than in the Elephants ; bnt in 
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