The _corpus striatum_ forms a thin broad ridge, which passes ventrally. This structure consists of twenty-five large pyramidal cells which lie in the posterior lateral dorsal section, and of from ten to fifteen pyramidal cells which are located in the rest of the section. In addition to these two groups there are many cells about 5 millimeters in diameter. These lie, six or more, in a nest imbedded in neuroglia. There is a thin layer of spindle cells near the ventral line. The outer nerve nest, or nerves amygdalis, lies in the posterior lateral ventral part. It is covered by a thin membranous layer. Its cells are pyramidal in shape and are from 10 to 15 millimeters in diameter. The cells terminate in spindle form toward the periphery. Nerve fibers extend from the anterior commissure. The outer wall of the corpus striatum consists of the following layers: An outer white layer consisting of fine medullated nerve fibers imbedded in a ground substance containing numerous nerve cells. A layer of ganglionic cells, consisting of pyramidal cells from 10 to 15 millimeters in diameter, of other round cells 20 millimeters in diameter, and finally of cells only 5 millimeters in diameter. This layer forms a reddish line in the dorsal portion of the corpus striatum. These layers form part of the median and the posterior cerebral wall of the lateral ventricle. The lateral ventricle is closed except for a slit-like opening behind the posterior commissure. This is the foramen of Monro, through which the lateral ventricle communicates with the middle, or third, ventricle. The _choroid plexus_ is found at the base of the lateral ventricle. The wall of the lateral ventricle becomes thinner near the region of the transverse commissure on the surface toward the middle brain. At this point the pia mater and the ependyma, or the lining cells of the ventricular membrane, form the major part of the wall. The domestic fowl does not have the hippocampus. The wall of the middle ventricle consists of an outer white layer, which is arranged similarly to that of the corpus striatum. The ventral rim of the wall is formed by a spiral band which consists of fine medullated fibers, in which are imbedded a few cells. The _processus cerebri mammillares_ are also called the tubercula olfactoria. From these structures extend forward the olfactory nerves, the posterior roots of which may be traced to the walls of the lateral ventricles. The structure of the processus cerebri mammillaris is made up of five layers as follows: An outer layer, which consists of colorless olfactory fibers extending in all directions. A granular ground substance layer, in which are imbedded a few cells. A thicker granular layer, on the inner edge of which are twenty large pyramidal cells with processes pointing outward. A layer of closely packed cells, in which are fine medullated nerve fibers. These cells are about 5 millimeters in diameter. An innermost layer of ependymal cells.