ordinary Ruminants they are partially joined by bony confluence, which rarely
extends to the proximal extremities ; in the Camel and Llama the anchylosis o f
the radius and ulna is so complete, that no trace o f their original separation can
be perceived, and the olecranon appears but as a mere process o f the radius.
In the Macrauchenia the anchylosis o f the radius and ulna is also complete,
but the boundary line o f the two originally distinct hones is very manifest, and the
proportion which each contributes to the great articulating surface for the distal
end o f the humerus is readily distinguishable. About a sixth part o f this surface
is due to the head o f the radius, which enters into the composition o f the anterior
and outer part o f the articulation, and its ex tent is defined b y a depressed line
describing a pretty regular curve, with the concavity directed forwards and a
little outwards, (o, fig. 1, PI. X .) Just below the articular surface a strong
triangular rugged protuberance projects from the front o f the head o f the radius,
for the attachment o f the tendon o f the biceps. T h e line o f separation o f the radius
and ulna is indicated on the inner side o f the head o f the radius by a deep and
narrow fissure extending downwards from below the anterior part o f the articulating
surface ; and on the outer side h y a broad groove leading upwards to a deep
pit near the proximal end o f the antibrachium. W e may se e by the direction of
the head o f the radius which is thus defined, that it crosses obliquely in front ot
the ulna, as in the Elephant, Hippopotamus, and other Pachyderms, and that
the bones are anchylosed in the prone condition : below this fissure and groove,
which mark the interosseous line, the radius and ulna become blended together
into one compact hone, which is flattened from before backwards, with a well
marked ridge on the outer side ; and excavated hy a sing le medullary cavity,
the compact walls o f which present a general thickness o f one-third o f an inch.
The proximal articular surface or sigmoid cavity o f the antibrachium, constituted
as above described, resembles that o f the Palæothere, Tapir, and the
generality o f the Pachyderms in having two depressions, instead o f three, as in
the Anoplothere, and Ruminants, The Hippopotamus has a sligh t tendency to
the latter structure, which is also le ss marked in the Camel than in the ordinary
Ruminants. In its general form the sigmoid cavity o f the Macrauchene resemb
le s that o f the Hippopotamus more than tliat o f the Camel. In tlie Camel this
articular surface is traversed transversely hy a broad, shallow, and sligh tly
roughened tract, which divides the smooth surface o f the jo int into two parts,
one forming the anterior horizontal surface due to the conjoined radius and ulna,
the other forming the vertical concave surface on the anterior part o f the base
o f tlie olecranon. In the Hippopotamus there is, as it w'ere, an attempt at a
similar division o f the articulating surface at the proximal end o f the antlbra-
chial hones ; a deeper and rougher depression encroaches upon the articulation
from its outer side, but stops when it has reached half-way across. In the