OSTEOLOGY AND DENTITION OF HYLOMYS. 465 
xiphosternum is a dorso-ventrally flattened rod of bone, slightly expanded at its two 
extremities, and about the length of the first and second mesosternal pieces, with an 
obscure longitudinal ridge on its outer surface. 
The humerus (fig. 14) is a rather short bone, only a very little shorter than the ulna. 
It is strong, and marked by a not very prominent deltoid ridge, in which region the 
bone is slightly laterally compressed. It has a rather large supracondylar foramen, 
which is wider behind than in front. The ectocondylar ridge does not extend on to 
the shaft, but forms a short eminence, with the surface external to it concave. The 
anconeal fossa is rather shallow. 
The shaft of the radius arches over the ulna, but the bones are separated by only a 
very narrow interval. The wna is a third the length of the radius longer than that 
bone. The olecranon is large, strong, and incurved, externally convex, and internally 
concave. Its posterior extremity is divided into two surfaces, there being a lower 
rough surface for the attachment of the triceps extensor muscle. 
The carpus is provided with a scapholunare and os intermedium and a large pisiform 
bone, resembling in miniature the pisiform of a Bear. The longest metacarpal bone is 
one third the length of the ulna. The first metacarpal is but little longer than the 
second, which reaches only to the anterior extremity of the middle third of the third 
metacarpal, which is of the same length as the fourth, which, in its turn, is twice as long 
as the fifth. 
The innominate bone (fig. 16) is long and narrow, with an elongately oval obturator 
foramen, with the very small symphysis pubis posterior and inferior to the foramen, 
with the tuberosity of the ischium nearly immediately above it, but the two sepa- 
rated from each other by the greatest width of the innominate bone, which here forms 
a triangular, externally concave, surface, with its posterior margin concave from behind 
forwards. The outer surface of the i/iwm is concave; and the spine of the ischium 
forms a well-marked lesser sciatic notch with the smooth surface for the tendon of the 
obturator internus muscle well displayed. 
The femur (fig. 17) is short and strong, with the muscular ridge continuous with the 
great trochanter, and passing down one half the length of the bone. The neck is very 
well defined. The patella is an elongated oval. 
The tibia and fibula (fig. 18) are completely united throughout one half of their 
extent; and in front, at their united extremity, there is a rather deep pit. The outer 
surface of the tibia, immediately below the knee-joint, forms a sharp ridge of bone, 
which is folded outwards with a deep concavity external to it. The fibula is very deli- 
cate; and where not united to the tibia, the two bones enclose a very much elongated 
oval space, In the specimen before me the epiphyses of the upper extremity of the two 
bones have completely united, while the upper extremities of the shafts are distinct. At 
the lower end the epiphyses of the two bones have disappeared. The calcaneum is a 
long rod-like bone, with its under surface rounded from side to side, but longitudinally 
quite flat, projecting only a short way behind the bones of the lower leg. 
