. Anthropology . ch—called the olfactory bulb—lies longi-tudinally in a depression on the surface of the anterior lobe; thesecond are the optic, whose decussation at the median line is calledthe chiasma. When Ave place the encephalon on its upper or convex surface,and remove the cerebellum and pons varolii by a transverse sectionpassing between the junction of the latter with the cerebralpeduncles, the whole inferior surface of the two hemispheres isexposed to view (Fig. 15). At the junction of the anterior thirdwith the posterior two-thirds is seen a deep transverse fissure,with its concavity
. Anthropology . ch—called the olfactory bulb—lies longi-tudinally in a depression on the surface of the anterior lobe; thesecond are the optic, whose decussation at the median line is calledthe chiasma. When Ave place the encephalon on its upper or convex surface,and remove the cerebellum and pons varolii by a transverse sectionpassing between the junction of the latter with the cerebralpeduncles, the whole inferior surface of the two hemispheres isexposed to view (Fig. 15). At the junction of the anterior thirdwith the posterior two-thirds is seen a deep transverse fissure,with its concavity looking backwards. This is the fissure ofSylvius (A, Fig. 16). The portion in front is the inferior surfaceof the frontal or anterior lobe; that behind is the inferior surfaceof the posterior lobe, which is separated into two well-marked Chap, in.] EXTERNAL SURFACE OF HEMISPHERES. 103 and unequal portions, the one with its convexity looking for-wards and outwards, which is the inferior region of the temporo-. FiG. 15.—Inferior surface of the encephalon: A, Anterior or frontal lobe; 13, Temporo-sphenoidal portion of the posterior lobe : A and B are separated by a fissure with itsconcavity looking- backwards—the tissure of Sylvius. C b, Cerebellum ; M, Sectionof the spinal cord where it joins the medulla oblongata ; VI, Annular protuberance —at its anterior border are seen the two cerebral peduncles ; C C, Coi^pus callosum—the dotted line is on the median or inter-hemispherical line; I to XII, The twelvepairs of encephalic nerves at their origin ; I, Olfactory nerve with its bulb ; II, Opticnerve, the union of which with that of the opposite side forms the chiasm a; 111,IV, VI, Nerves of motion of the globe of the eye ; V, Trigeminal, or fifth, supply-ing the muscles of expression ; XII, Hypoglossal nerve, the nerve of motion of thetongue. sphenoidal lobe, the other, posterior or concave, upon- which thecerebellum lies. The superior or convex surface of the hemispher
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