File talk:Adult human hypothalamus 02.jpg

The Hypothalamus (Fig. 720) includes the subthalamic tegmental region and the structures forming the greater part of the floor of the third ventricle, viz., the corpora mammillaria, tuber cinereum, infundibulum, hypophysis, and optic chiasma.

The subthalamic tegmental region consists of the upward continuation of the tegmentum; it lies on the ventro-lateral aspect of the thalamus and separates it from the fibers of the internal capsule. The red nucleus and the substantia nigra are prolonged into its lower part; in front it is continuous with the substantia innominata of Meynert, medially with the gray substance of the floor of the third ventricle.

It consists from above downward of three strata: (1) stratum dorsale, directly applied to the under surface of the thalamus and consisting of fine longitudinal fibers; (2) zona incerta, a continuation forward of the formatio reticularis of the tegmentum; and (3) the corpus subthalamicum (nucleus of Luys), a brownish mass presenting a lenticular shape on transverse section, and situated on the dorsal aspect of the fibers of the base of the cerebral peduncle; it is encapsuled by a lamina of nerve fibers and contains numerous medium-sized nerve cells, the connections of which are as yet not fully determined.

The corpora mammillaria (corpus albicantia) are two round white masses, each about the size of a small pea, placed side by side below the gray substance of the floor of the third ventricle in front of the posterior perforated substance. They consist of white substance externally and of gray substance internally, the cells of the latter forming two nuclei, a medial of smaller and a lateral of larger cells. The white substance is mainly formed by the fibers of the columns of the fornix, which descend to the base of the brain and end partly in the corpora mammillaria. From the cells of the gray substance of each mammillary body two fasciculi arise: one, the thalamomammillary fasciculus (bundle of Vicq d’Azyr), passes upward into the anterior nucleus of the thalamus; the other is directed downward into the tegmentum. Afferent fibers are believed to reach the corpus mammillare from the medial lemniscus and from the tegmentum.

Figure 1 Hypothalamic nuclei involved in vasopressin control. The hypothalamus surrounds the third ventricle ventral to the hypothalamic sulci.