NERVOUS SYSTEM. : 707 
and expand into posterior tuberosities. The ischia of 
Mammals may touch one another ventrally, but do not 
fuse in a symphysis; the pubic symphysis is almost invari- 
ably present. Only in Cetacea and Sirenia is the pelvis 
markedly rudimentary. 
The hind-leg consists of a thigh or femur, a lower leg 
with two bones—the tibia and the fibula, an ankle or 
tarsus, the sole-bones or metatarsals, the toes with several 
joints or phalanges. 
The head of the femur works in the acetabulum of the pelvis. Near 
the head are several processes or trochanters, serving for the insertion 
of muscles; in the rabbit there are three—the great trochanter, the 
lesser trochanter, and the third trochanter. : 
In front of the knee there is a sesamoid bone—the knee-pan or 
patella—and posteriorly there are smaller fabellz. 
In the lower leg, the tibia, which corresponds to the radius, is pre- 
axial, and ia the normal position interior ; the fibula, which corresponds 
to the ulna, is postaxial, and in the normal position exterior. There 
is no crossing of bones as in the forearm. In the rabbit the fibula is 
slender, and is fused distally with the tibia. 
In the mammalian tarsus there are two rows of bones, and a central 
bone interposed between the two rows on the inner or tibial side. . 
First }  Calcaneum Astragalus 
Row Jf, or Fibulare. or Tibiale. 
Centrale 
or Navicular, 
Tarsalia 5 and 4 Tarsale 3 Tarsale 2 Tarsale 1 
SECOND =Cuboid. or or or 
Row External Middle Internal 
Cuneiform. Cuneiform. Cuneiform. 
In the rabbit the first cuneiform and the corresponding hallux are 
wanting. There are thus only four metatarsals and digits. Each digit 
has three phalanges, and ends in a claw. 
Nervous system.—The brain has the usual five parts— 
cerebral hemispheres, optic thalami, optic lobes, cerebellum, 
and medulla oblongata, but the cerebral hemispheres cover 
the next two parts, and the cerebellum conceals the medulla. 
Of the brain membranes, the dura mater lines the cranial 
cavity, projecting longitudinally between the cerebral hemi- 
spheres, and transversely between the latter and the cere- 
bellum, while the vascular pia mater invests the brain 
closely. There are the usual twelve pairs of cranial 
nerves. The spinal cord gives off the usual spinal nerves, 
