Diseases of the nervous system .. . es and the pons, the trochlear nerve arises. The fifthnerve with its narrow motor and broad sensory divisions emerges from thelateral posterior portion of the pons. While, up to this point, the cranialnerves are isolated at the base of the brain, when the pons enters the medullaand the cerebellum begins, the origins of the cerebral nerves are close together,so that, for instance, tumors which here implicate the bones of the posterior MACROSCOPIC ANATOMY OF THE CENTRAL NERVOUS SYSTEM 25 groove of the skull or the cerebellum, even without attaining great devel
Diseases of the nervous system .. . es and the pons, the trochlear nerve arises. The fifthnerve with its narrow motor and broad sensory divisions emerges from thelateral posterior portion of the pons. While, up to this point, the cranialnerves are isolated at the base of the brain, when the pons enters the medullaand the cerebellum begins, the origins of the cerebral nerves are close together,so that, for instance, tumors which here implicate the bones of the posterior MACROSCOPIC ANATOMY OF THE CENTRAL NERVOUS SYSTEM 25 groove of the skull or the cerebellum, even without attaining great develop-ment, may cause multiple cranial nerve paralyses. The abducens emergesmedially from the transverse furrow between the pons and the medulla,while the facial and acoustic (VII and VIII) nerves appear at the sideof the medulla oblongata. The glosso-pharyngeal and vagus follow caudad. Bulbus olfactorius (I)Tractus olfactorius \ Chiasma opticumN. opticus (11) Polas frontalis Fissura longitudinalis cerebriSulcus olfactorius Hypophysis. Trigonxxm dfactorium r. oculomotonus (in) N. trochlearid(TV) . (V) !^. abducens(VI) N. facialis (yu) N. acusticus —(VIII) N. ^pharyngeus (IX) Fissura cerebri lateralis(Sylvii) Polus temporalis Substantia per-forata anterior ,_Infundibulum Fossa inter-—peduncularis(Tarini) •pedunculuscerebri Pons (Varoli) Floccvitus .^Plexus chorioideusventriculi quart i Foramen caecum Hemispha?riiim cerebelli N. hypoglo^us N. SDinalis I Medulla oblongataDecussatfo pyramidumMedulla spinalis Polus oCcTpitalfsFig. 17.—The Base of the Brain Showing the Origin of the Roots of the Craniai. basal surface of the cerebrum in its posterior division is covered by the cerebellum. while the spinal accessory and hypoglossal nerves arise from the lateral partsof the lowest portion of the medulla oblongata, the former, indeed, fromthe uppermost part of the cervical cord. The individual parts of the cere-brum and the cerebellum at the base of t
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