PALiEOSYOPS LEIDY, AND ITS ALLIES. 
295 
si)iiie. The centnun of the axis is very short ; its posterior siirfiice is slightly con- 
cave and very deep from above downwards. The under surface of the centrum is 
provided with a prominent keel, its surfiice being deeply excavated on each side of the 
latter. The keel is much longer and more prominent than in Rhinoceros. The ante- 
rior ai'ticular surface of the axis resembles closely that of the Khinoceros. The 
odontoid process is very long and conical, much longer than in the Tapir. The articu- 
lar surfaces for the atlas ai-e much more oblique to each other than in the Rhinoceros. 
They are triangular in outline, their extenial portion being very broad, becoming 
nai-row as they approach the middle of the vertebra. The neural canal of this ver- 
tebra has the same height as that of the Rhinoceros, but it is narrower, and the floor 
of the same has anteriorly a very conspicuous longitudinal tubercle. The axis of 
this species agrees with that of the Rhinoceros in not having interspinous foramina 
for the spinal nerves, which in Tapirus as in Eqnus come ofl‘ from the spinal cord 
through a special foramen in the axis. The form of the transverse process of the 
axis is. peculiar ; it is placed higher than in Rhinoceros, its vertebrarterial canal being 
on a line with the upper surface of the body, and instead of the transverse process 
arising from the middle of the canal, it is placed above it. so that its inferior root is 
nearly vertical. This is certainly a very jjeculiar character of the vertebra. 
Fourth cervical . — This is the only cervical vertebra posterior to the atlas which 
is preserved in the collection. Its most striking character is its high centrum, and 
this is apparently out of all proportion to the size of the arch. Compared with that 
of the cervical of the Rhinoceros the body is very much shorter ; its height is about 
the same, but the breadth of the centrum is very much greater. This vertebra is 
slightly opisthocoelous, the anterior convexity being much less than in that of 
the Rhinoceros. 
The anterior convexity, moreover, is marked by a transverse depression. The 
neural opening is slightly smaller than in Rhinoceros. The basal portion of the 
transverse processes pierced by a large vertebrarterial canal, and the diapophysis is 
much thinner and shorter than the parapophysis. The neural arch of this cervical 
is low and broad. The prezygapophyses are very large, and oblique and their in- 
ferior ends do not become concave as in those of the Rhinoceros. The peduncular 
portion of this cervical is lower than in that of the Rhinoceros. The postzyga- 
j)ophysis has been damaged in this vertebra. There is also in the collection a 
seventh cervical belonging to a smaller species than P. paludosus. This has the 
general form of the vertebra already described, its centrum is more opisthocoelous 
tlian the latter. The diapophysis only is present. The vertebrarterial canal is, as 
usnal, wanting in this vertebra. 
Dorsals, (No. 10,282.) PL XIII, flgs. 32-35. There are six dorsal vertebrm in 
the collection in^nldition to the cervical last described, all belonging to the same indi- 
^ndual. The most striking differences between this series of dorsals and the same 
vertebra} in Rhinoceros, are the dimensions of the centra and the great extension of 
