The lamina cinerea and tuber cinereum form the inferior gray commissure of the fore-brain.
The hypophysis (pituitary body, Fig. 21) is composed of two lobes bound together by connective tissue. A sheet of dura mater (diaphragma sellce) holds them in the hypophyseal fossa. The anterior lobe, the larger, is derived from the epithelium of the mouth cavity; and, in structure, resembles the thyreoid gland. Its closed vesicles, lined with columnar epithelium (in part ciliated), contain a viscid jelly-like material (pituita), which suggested the old name for the body. The anterior lobe is hollowed out on its posterior surface (kidney-shape) and receives the posterior lobe, the infundibulum, into the concavity. The hypophysis has an internal secretion which appears to stimulate the growth of connective tissues and to be essential to sexual development. The active hormone is found in the posterior lobe, the pars nervosa; the anterior lobe contains only a colloid, eosinophile material. According to Harvey Cushing, an excess of this hormone, in youth, causes giantism; in the adult it produces acromegaly. While, on the other hand, deficiency in childhood is associated with small stature, excessive fat and eunuchism; and, if the deficiency develop in the grown-up, there is sexual atrophy and disappearance of the signs of adolescence.
Corpora Mam.millaria (Figs. 21 and 3i).—Two white bodies (corpora albicantia), as large as a small pea, are situated one on either side of the median line, between the tuber cinereum and the pigmented gray matter of the posterior perforated substance.
Being produced by the division of a single, median body in the embryo, they remain in the adult in close apposition. Each is formed superficially by a loop in the columna of the fornix and is, therefore, composed of white substance at the surface. There is gray matter in the interior which forms a round medial and a crescentic lateral nucleus (Fig. 58). In the medial nucleus the fornix fibers terminate and an ascending bundle rises, called the fasciculus mammillaris princeps; this bundle divides Y-like into mammillo.'thalamic (or thalamo-mammillary) bundle, which ends in the thalamus, and mammillo-tegmental (or tegmento-mammillary) bundle, which descends to the teg mentum of the mid-brain, pons, etc. The lateral nucleus of the mammillary body gives rise to a small fasciculus which terminates in the tegmentum of the mid-brain; it is called the peduncle of the mammillary body.
Immediately behind the corpora mammillaria is the posterior perforated substance (Figs. 21 and 31). This is the exposed part of the substantia nigra of the mid-brain, perforated for the passage of the postero-median ganglionic arteries. The pons and bases pedunculi bound it behind. Issuing from the inner side of the basis pedunculi is the large oculomotor nerve; and coursing over its surface from behind forward, is the smaller trochlear nerve. The bases pedunculi will be described with the mid-brain to which they belong.