874 



THE NERVE SYSTEM 



sensor decussation. Cephalad of this decussation the lemnisci are two bundles 

 of fibres coursing on either side of the raphe between the olives, and just dorsad 

 of the pyramids; their further course toward the cerebrum will be described 

 farther on. 



HYPOGLOSSA^ 



NUCLEUS CUNEATUS 



HEAD OF DORSAL HORN 

 ROOT OF TR1FAC1AL NERVE 



MOTOR NUCLEUS OF MIXED 



NERVES 



ACCESSORY HYPOGLOSSAL 



NUCLEUS 



HYPOGLOSSAL NERVE 



/ < ~ : *&i$F' ***!$$&( VENTRAL 

 LEMNISCUS VENTROMEDIAN ARCIFORM PYBAMID 

 FISSURE NUCLEUS 



FIG. 642. Transverse section of the medulla oblongata at the middle of the olives. The roof of the 

 fourth ventricle is not represented. (Testut, after Duval.) 



With the extension of the central gray to form the floor of the fourth ventricle, 

 the caput cornu dorsale is displaced ectad so as to almost reach the surface, 

 where it forms a projection, the funiculus lateralis (Rolandi}, which enlarges 

 cephalad into a distinct prominence, the tuberculum cinereum. At a higher level 



FOURTH VENTRICLE. NUCLEUS INTERCALATU8 FASCICULUS SOLITARIUS 



/AND ITS NUCLEUS 

 NUCLEUS HYPOGLOSSI \ \ NUCLEUS VAG , 



DESCENDING ROOT VIII 



SUBST. 

 GELATINOSA 



SPINAL ROOT OF 

 TRIGEMINUS 



VAGUS NERVE 



DORSAL ) ACCESSORY 



f OLIVE 



MESIAL ) 



XT. ARCUATE FIBERS 



HYPOGLOSSAL NERVE 



HILUM OLIV/E 



ARCUATE NUCLEUS 



FIG. 643. Trans-section of the medulla oblongata at about the middle of the olive. 



the caput is separated from the surface by the spinal root of the trigeminal nerve and 

 by the external arcuate fibres (Fig. 643). The cervix of the cornu becomes broken 

 up into a reticular formation by the decussating fibres. A portion of the base 

 is placed ectad of the nucleus funiculi cuneati and is called the accessory cuneate 

 nucleus, supposed to be a continuation of Clarke's column. 



