The spinal cord is relatively large. There are ten pairs of spinal nerves connected with it, the first corresponding with the hypoglossal nerve in mammals. Each is connected to a sympathetic ganglion, there being a quite well-developed double sympathetic nerve chain. Spinal nerves Nos. 2 and 3 on each side unite and then branch, forming a brachial plexus ; Nos. 6 to 10 also form a sciatic plexus, giving nerves to the hind limb and lumbar region.
The olfactory lobes are quite large the thalam-encephalon is large and the cerebral hemispheres are poorly developed—it takes the animal a very long time to learn by experience, although it can be tamed. The optic lobes are large, the animal relying almost entirely upon its sense of sight to obtain food. Even this activity seems to be almost purely reflex for it flicks its tongue out quite impartially whether it sees moving prey or moving cotton wool, and yet will entirely disregard piles of inert food.
The cerebellum is small, since the animal ’s shape renders it easy to remain horizontal when swimming, and its low centre of gravity keeps it stable when landing after a leap, so that it does not require a delicate control of balance. The medulla is almost as large as the fore-brain, indicating that most of the animal ’s activities are reflexes.