Third, broader granular, or molecular layer, having on its inner surface a row of large pyramidal cells which are both small and large and which send their dendrites into the olfactory glomeruli. Their points are directed outward. Fourth, a layer of round cells tightly pressed together and measuring about 5 microns in diameter. Between these cells are very fine nerve fibers. [Illustration: FIG. 75.—The brain of a hen. Photograph. _A._ Upper surface of the brain. 1, Medulla oblongata. 2, Calamus scriptorius. 3, Cerebellum. 4, Optic lobes. 5, Transverse fissure. 6, Longitudinal fissure. 7, Upper surface of the left cerebral lobe. 8, Upper surface of the right cerebral lobe. 9, Lateral pillar of the cerebellum. _B._ The posterior surface of the eyeball. 10, The sectioned surface of the optic nerve. _C._ The inferior surface of the brain. 11, Corneo-scleral juncture. 12, The cornea. 13, The sclera. 14, The optic nerve. 15, The optic chiasm. 16, The olfactory lobes. 17, The medulla oblongata. 18, Tuber cinererum et infundibulum. ] Fifth, a layer of epithelial cells. The peripheral fibers and the nerve cell layers near the hemispheres disappear so that the basic substance of the trabecula with the hemispheres form the entire lobe mass. On the lower surface of the hemispheres there is a long bundle of nerve fibers which enter into the substance of the olfactory lobes and there disappears. These fibers are medullated. Non-medullated fibers enter into the makeup of the olfactory trunk. The original center of the olfactory nerve is not in the hemisphere, but in the same location as the optic nerve. This nerve trunk consists of very fine non-medullated fibers. The nerves of smell are therefore not peripheralistic nerves. The nerve fibers are distributed to the mucous surface of the turbinated bones. Toward the front they form an expanded prolongation. The olfactory nerve, as it emerges from the cone-like anterior tip of the cerebrum, is of considerable thickness and extends along with the median dorsal artery of that region above and to the inside of the orbit, under the thin bony structure. Before its termination into the posterior turbinated bones, it is crossed by the superior maxillary division of the fifth pair of cranial nerves. It extends as far as the pituitary membrane of the turbinate bones upon which its filaments are distributed radially. =The Opticus.=—The nervus opticus (Fig. 75, No. _C_, 14) the second cranial, is the nerve of sight. The optic lobe, or tuberculum bigeminum lies at the base of the brain on each side of the optic tract.