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 fabellae. 



In the lower leg, the tibia, which corresponds to the radius, is pre- 

 axial, and in 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 -i Calcaneum Astragalus 



Row / or Fibulare. or Tibiale. 



Centrale 

 or Navicular. 



\ Tarsalia 5 and 4 Tarsale 3 Tarsale 2 Tarsale i 



SECOND I = 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, 



47 



