The basal ganglia consists of masses of gray mater or nuclei, viz. the caudate and lenticular nuclei, claustrum and amygdaloid within the cerebral hemisphere. The caudate and lenticular nuclei are incompletely separated by tracts of white mater called the internal capsule . The internal capsule actually consists of a masses of projection fibres connecting cerebral cortex with lower levels of brain and spinal cord.
The caudate nuclei lies medially and its head forms the anterior part of the floor of the lateral ventricle and becomes continuous with the amygdaloid nucleus. The lenticular nucleus is shaped like a biconvex lens and medially it is separated from the caudate nucleus by the internal capsule and laterally covered by a thin band of white mater called the external capsule that separates it from a thin band of gray mater, claustrum that is dentated laterally. The lenticular nucleus is subdivided into an external part, the putamen and an internal part the globus pellidus.
The amygdaloid nucleus is a small ovoid mass of gray mater situated lateral to the posterior cornu of the lateral ventricle and is believed to be a correlation centre for olfactory and somatic sensibilities.
The basal ganglia is an important motor correlation centre in lower vertebrates and forms an important part of the extra-pyramidal system, through its connections to substantia nigra and red nucleus . It also plays part in regulating tonus of voluntary musculature by modifying the activities of the lower motor neurons and also control automatic associated movements.
