MEDULLA OBLOXGATA. 



341 



of the cerebello-spinal fasciculus of the cord, some from the gracile and 

 cuneate nuclei, and some from other nuclei in relation with the sensor)' 

 roots of the cranial nerves. 



The cerebral nerves of the medulla (and pons also) are arranged in 

 general as follows. The ventral roots arise from groups of cell bodies, 

 the nuclei of the nerves, situated beneath the floor of the ventricle near the 

 median line. The nucleus of the hypoglossal nerve is seen in Fig. 396. 

 The lateral roots arise from nuclei more deeply placed and further from 

 the median line; their fibers may pass upward and inward toward the 

 ventricle before turning downward and outward to leave the brain. The 

 nucleus atnbiguiis (Fig. 396) gives rise to the lateral roots of the vagus and 

 glossopharyngeus. Like 

 the motor cells of the 

 spinal cord, those of the 

 brain are also in connection 

 with descending fibers of the 

 pyramidal tract. The dor- 

 sal roots on entering the 

 brain generally divide into 

 a short ascending branch 

 and a longer descending 

 one. The tractus solitari- 

 us (Fig. 396) contains the 

 descending fibers of the 

 vagus and glossopharyn- 

 geus; the large spinal tract 

 composed of the descend- 

 ing fibers of the trigeminus 

 is shown in Figs. 395 and 



396. The dorsal root fibers end in nuclei corresponding with the 

 gracile and cuneate nuclei of spinal nerves. Fibers from the internal 

 nuclei of the cerebral sensory nerves join the lemniscus and proceed 

 toward the hemispheres. 



PONS. 



The ventral swelling characteristic of the pons is due to the transverse 

 fibers of the brachium pontis (Fig. 391). These cross beneath and through 

 the pyramidal bundles. Some of them arise from numerous groups of 

 nerve cells scattered among them, the nuclei pontis, and pass to the same 

 or opposite side of the cerebellum; others descend from the cerebellum to 

 the same or opposite side of the pons. The fibers of the lemniscus and 



lem. 



FIG. 396. SECTION OP THE MEDULLA. (After Dejerine.) 

 c. r., Corpus restiforme; f. c. o., cerebello-olivary fibers; lem., 

 lemniscus; n. am., nucleus ambiguus; n. h., nucleus hy- 

 poglossi; ol., olive; py., pyramid; t. s., tractus solitari- 

 us; f. s. n. t., tractus spinalis nervi trigemini; v., fourth 

 ventricle. 



