Basal Ganglia and Related Structures 159

Caudate Nucleus. The caudate nucleus resembles an elongated and curved exclamation mark. Its main part is an expanded head directly continuous with a smaller and attenuated body that merges into an elongated tail. The head bulges into the anterior horn of the lateral ventricle and forms its sloping floor. The caudate nucleus is separated from the lentiform nucleus by the anterior limb of the internal capsule, but the separation is incomplete because the head of the caudate nucleus and the putamen are connected, especially anteroinferiorly, by bands of gray matter traversing the white matter of the anterior limb. This admixture of gray and white matter produces the striated appearance that justifies the term “corpus striatum” applied to these nuclei. The head tapers into the narrower body that lies in the floor of the central part of the lateral ventricle, lateral to the superior surface of the thalamus and separated from it by a shallow sulcus lodging the stria terminalis and thalamostriate vein. The tail turns downward along the outer margin of the posterior surface of the thalamus, with the stria terminalis still lying in a slight groove between them. It then curves forward into the roof of the inferior horn of the lateral ventricle, where it separates from the thalamus and lentiform nucleus by the inferior part of the internal capsule and by fibers (including some from the anterior commissure) that spread into the temporal lobe.

Amygdaloid Body. The tail of the caudate nucleus ends in a small, almond-shaped expansion, the amygdaloid body, which is a complex of several small nuclei located in the forepart of the roof of the inferior horn of the lateral ventricle. The stria terminalis issues from the amygdaloid body and runs along the medial side of the caudate nucleus until it reaches the vicinity of the ipsilateral interventricular foramen. Here, some of its fibers join the anterior commissure, others pass to the “septal” region adjacent to the lamina terminalis, and the remainder descends to the hypothalamus and anterior perforated substance.

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