. The animans and man; an elementary textbook of zoology and human physiology. an inner coat, the arachnoidmembrane. This membrane containslarge spaces filled with a fluid (thecerebro-spinal fluid). This, like theserous fluids surrounding the heart andlungs, is a protective fluid. Structure of the brain (fig. 179 Aand fig. 179 B).—Like the brain of thecat (see page 67) the human brainconsists primarily of three parts, thefore brain, mid brain, and kind fore brain or cerebrum is large andconspicuous. It comprises nine-tenthsof the brains bulk and almostcompletely covers the other part
. The animans and man; an elementary textbook of zoology and human physiology. an inner coat, the arachnoidmembrane. This membrane containslarge spaces filled with a fluid (thecerebro-spinal fluid). This, like theserous fluids surrounding the heart andlungs, is a protective fluid. Structure of the brain (fig. 179 Aand fig. 179 B).—Like the brain of thecat (see page 67) the human brainconsists primarily of three parts, thefore brain, mid brain, and kind fore brain or cerebrum is large andconspicuous. It comprises nine-tenthsof the brains bulk and almostcompletely covers the other disproportion in size gives someindication of its very great importanceas compared with that of the otherparts. The cerebrum is characterizedby many convolutions. Seen fromabove its right and left halves (hemi-spheres) are separated from each other NERVOUS SYSTEM 359 by a deep fissure. They are connected below by a broadnerve mass, the corpus callosum. From the under surface of the brain, the other parts canbe made out. The fissure continues back to the mid ncl FIG. 179 B. Ventral view of brain, showing origin of cranial nerves. I,olfactory; II, optic; III, ocular motor; IV, patheticus; V, trigeminal;VI, abducent; VII, facial; VIII, auditor}-; IX, glossopharyngeal;X, pneumogastrie; XI, spinal accessory; XII, hypoglossal; ncl, 1stspinal nerve. (After Martin.) The two long olfactory lobes project forward from in frontof the mid brain. The optic nerves arise from it. Posteriorto the mid brain lies the hind brain, consisting of the largewrinkled lobes of the cerebellum (fig. 179 A, c), lying appar- 3<5° THE ANIMALS AND MAN ently one on either side of the medulla oblongata. The twolobes of the cerebellum are connected by a mass of nervefibers called the pons varolii (fig. 179 A). The medulla ob-longata (fig. 179 A, mo) is continued ventrally into the spinalcord.
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