The importance of the brain in this animal is readily seen on comparing it in size with the spinal cord, which bears two sympathetic chains running along the dorsal aorta. There are many other pairs of spinal nerves \ hich are joined to other very small sympathetic nerve networks in the body cavity, the most prominent being near the kidneys and known as the solar plexus.
The largest part of the brain is the cerebral hemispheres, which almost completely overlap the mid-brain.
The hemispheres have their surface area slightly increased by fissures and traces of furrows termed sulci, and they are divided by these fissures into lobes, corresponding to those in man.
The walls of the thalamencephalon are large optic thalami. Although not very intelligent, the animal learns to recognize friends, can be tamed and taught tricks, although it takes a long time to learn by experience.
The optic lobes of the mid-brain are divided each into two, forming the corpora quadrigemina. The crura cerebri are prominent.
The cerebellum is divided into five lobes which are thrown into folds—a condition related to the facts that when the animal runs it has a habit of turning sharply, and its centre of gravity is high, so that a very fine control of muscles to maintain balance is essential. The pons is also prominent, forming the connection between the two halves of the cerebellum.