The _hypophysis_ (Fig. 62, No. _C_, 20) lies back of the chiasm, or optic commissure, and below the middle of the third ventricle. The infundibulum, a pedicle-like structure, connects the hypophysis with the third ventricle of the cerebri. It contains a cavity and forms an extension of the third ventricle. The hypophysis is divided into two lobes, an anterior and a posterior. The _third ventricle_ communicates anteriorly with the lateral ventricles of the cerebri through the foramen of Monro, and posteriorly with the fourth ventricle through the aqueduct of Sylvius. The posterior walls of the third ventricle are relatively thick and form the posterior brain commissure. The wall is thin from the commissure to the chiasm. Within it lie two ridges, which connect the two hemispheres with the corpus callosum, and, farther anteriorly, with the anterior cerebral commissure. The space from the third ventricle and to the anterior commissure is called the laminæ terminales. The _pineal gland_, located between the cerebri and the cerebellum, lies against the choroid plexus, which covers the highest point of the third ventricle. The _cerebrum_ is divided by a deep longitudinal fissure into two hemispheres. The cerebrum is shaped somewhat like the heart on a playing card. The lower face is somewhat flattened. The upper and lateral sides are not provided with convolutions or sulci, but are smooth. The fissure of Sylvius is faintly marked on the inferior face. The olfactory lobes appear well developed and are relatively large for the size of the brain. They lie close together on the extreme anterior portion in the median line. The _olfactory cerebral crura_ emerge from the cranium at the upper angle between the posterior wall, the roof, and the septum of the orbit, and pass through the olfactory foramina and in grooves on the upper part of the septum; then passing forward they penetrate the frontal structure and are finally distributed over the turbinated mucous membrane. The _corpus striatum_ is large; it occupies nearly the entire floor of the ventricles. The _anterior commissure_ is found between the hemispheres. Its middle part lies in the lamina terminalis on the division between the anterior and the middle brain, and close to the thalami optici. Its side extensions are rounded masses called the nervi amygdales. The _corpus callosum_, quite rudimentary, lies on the posterior dorsal rim of the anterior commissure.