Gray Matter of the Fore-Brain

The chief grey matter of the fore-brain comprises:

(1)the ganglia at the base;
(2) the surface grey matter or cortex.

(1) The basal ganglia, two on either side, are the thalamus and the corpus striatum.

Thalumus. - The thalamus is a large ovoid mass which occupies the greater part of the side wall of the third ventricle. Anteriorly its narrower extremity projects into the floor of the lateral ventricle (Fig. 61), while posteriorly its broader end overhangs the superior quadrigeminal body. On the posterior end are three well-marked swellings; the internal is termed the pulvinar, the external is the external geniculate body, and the intermediate (posterior) is the internal geniculate body (Fig. 55). The two thalami are joined to one another across the middle line by a band of grey matter-the middle commissure (Fig. 63).

The thalamus is a great terminal nucleus for the sensory fibres ascending from the spinal cord and the hinder parts of the brain. Round its cells most of the fibres of the mesial fillet end by arborisation.

It receives also fibres from cells of the cerebral corex. Its chief emerging fibres are arranged in four great groups or stalks: (a) anterior, to the frontal lobe; (b) posterior, to the occipital lobe; (c) inferior, to the island of Reil and temporal lobe; (d) outer, to the parietal lobe. Many fibres also pass from and to the corpus stratium.