290 THE OSTEOLOGY OF ELOTHERIUM. 
outward, as well as downward; their bases are separated by a broad and deep grooye, 
which is continued upward upon the posterior side of the neural spine. 
The third cervical vertebra also bears a considerable resemblance to that of Aippopo- 
famus, differing only in some points of detail. The centrum is short, heavy and moder- 
ately opisthoccelous, depressed, but increasing posteriorly in vertical thickness. It bears 
-a strong yentral keel, which terminates behind, as in the axis, in a trifid hypapophysis. 
The pedicels of the neural arch are not, as in the pigs, pierced by foramina for the 
spinal neryes; they are low and short, but very thick, and the neural canal is strikingly 
small. The dorsal side of the arch is short, broad and nearly flat. The neural spine is 
remarkably well-developed (when the anterior position of the vertebra is taken into 
account), rising as high as that of the axis. It is rather thin and compressed, although its 
base occupies the whole fore-and-aft length of the arch. From the base, however, it rapidly 
tapers upward and terminates ina small, rough tubercle. In Hippopotamus the third 
cervical has an even better developed neural spine, not higher, but broader and less 
tapering than in Llotherium. The prezygapophyses are large, oblique and somewhat 
conyex ; they are placed very low, so that their inferior margins are separated from the 
centrum only by narrow notches. The posterior zygapophyses are much larger and 
more prominent than the anterior pair; they are also less oblique in position and are 
raised higher above the centrum, corresponding to the posterior elevation of the neural 
arch. The transverse. process is a compressed plate, which has no great vertical height, 
but is well extended from before backward, exceeding the centrum in length; the pos- 
terior portion of the process is thickened and recurved, ending in a rugose hook. The 
absence of any distinctly marked diapophysial element distinguishes this vertebra from 
the corresponding one of Hippopotamus and Sus, and in the latter genus the inferior 
lamella is more slender and rod-like, while the spinal nerves make their exit through 
foramina in the pedicels of the neural arch. 
The fourth cervical vertebra is different, in many respects, from the third. The 
centrum is somewhat shorter and is less distinctly carinate on the ventral side, but is more 
decidedly opisthoccelous. The neural arch is remarkably short in the antero-posterior 
dimension, so that the articular faces of the postzygapophyses actually extend forward 
beneath those of the anterior pair, which gives to the pedicel of the neural arch, when 
seen from the side, a curiously notched appearance. The neural spine is higher, but 
more slender and recurved than that of the third cervical. The transverse process is 
altogether different in shape from that of the latter. It has, in the first place, a very 
prominent diapophysial element, which projects outward as a heavy, depressed bar, 
thickened, rugose, and slightly upcurved at the distal end. In the second place, the 
inferior lamella is much higher vertically, but decidedly shorter from before backward, 
