. A text-book of physiology : for medical students and physicians . AL NERVOUS SYSTEM. The Histological Evidence.—The histological results supple-ment in a very satisfactory way the findings from physiology andpathology. The retina itself, considered from an embryologicalstandpoint, is an outgrowth from the brain vesicles, and is there-fore an outlying portion of the central nervous system. The opticfibers, in terms of the neuron doctrine, must be considered asaxons of the nerve cells in the retina. If, therefore, an eye is enu-cleated or an optic nerve is cut the fibers connected with thebrai
. A text-book of physiology : for medical students and physicians . AL NERVOUS SYSTEM. The Histological Evidence.—The histological results supple-ment in a very satisfactory way the findings from physiology andpathology. The retina itself, considered from an embryologicalstandpoint, is an outgrowth from the brain vesicles, and is there-fore an outlying portion of the central nervous system. The opticfibers, in terms of the neuron doctrine, must be considered asaxons of the nerve cells in the retina. If, therefore, an eye is enu-cleated or an optic nerve is cut the fibers connected with thebrain undergo secondary degeneration and their course can betraced microscopically to the brain. By this means it has beenshown that in man and the mammalia there is a partial decus-sation of the optic fibers in the chiasma. The fibers from theinner side of each retina cross at this point to the opposite optictract; those from the outer side of the retina do not decussate, Occipital lobe. Occipito-thalamic colliculus. Lateral Retina. Fig. 92.—Diagram to indicate the general course of the fibers of the optic nerves and thebilateral connection between cortex and retina. but pass into the optic tract of the same side. The fibers of theoptic tract end mainly in the gray matter of the lateral genicu-late body, but some pass also to the thalamus (pulvinar) andsome to the superior colliculus of the corpora quadrigemina. SENSE AREAS AND ASSOCIATION AREAS. 209 These locations, therefore, particularly the lateral geniculates,must be considered as the primary optic centers. From thesepoints the path is continued toward the cortex by new neuronswhose axons constitute a special bundle, the occipitothalamicradiation, lying in the occipital part of the internal capsule(see Fig. 82, D). A schema representing this course of theoptic fibers is given in the accompanying diagram (Fig. 92).According to this schema, the general relations of each occipitallobe
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