784 



NEUROLOGY 



fibers are continued directly from the gracile and cuneate fasciculi into the interior 

 peduncle. 



(6) Fibers from the terminal sensory nuclei of the cranial nerves, especially the 

 vestibular. Some of the libers of the vestibular nerve are thought to continue 

 directly into the cerebellum. 



(7) Fibers from the ventral spinocerebellar fasciculus. 



(8) The existence of fibers from the cerebellum (cerebellobulbar, cerebellooliv 

 and cerebellospinal) to the medulla and spinal cord is very uncertain. 



13.. 



FIG. 700. The formatio reticularis of the medulla oblongata, .shown by a transverse section passing through the 

 middle of the olive. (Testut.) 1. Anterior median fissure. 2. Fourth ventricle. 3. Formatio reticularis, with 3', 

 its internal part (reticularis alba), and 3", its external part (reticularis grisea). 4. Raph6. 5. Pyramid. 6. Lemniscus. 

 7. Inferior olivary nucleus with the two accessory olivary nuclei. 8. Hypoglossal nerve, with 8', its nucleus of origin. 

 9. Vagus nerve, with 9', its nucleus of termination. 10. Lateral dorsal acoustic nucleus. -11. Nucleus ambiguus 

 (nucleus of origin of motor fibers of glossopharyngeal, vagus, and cerebral portion of spinal accessory). 12. Gracile 

 nucleus. 13. Cuneate nucleus. 14. Head of posterior column, with 14', the lower sensory root of trigeminal nerve. 

 15. Fasciculus solitarius. 16. Anterior external arcuate fibers, with 16', the nucleus arcuatus. 17. Nucleus lateralis 

 18. Nucleus of fasciculus teres. 19. Ligula. 



Formatio Reticularis (Fig. 700). This term is applied to the coarse reticulum 

 which occupies the anterior and lateral districts of the medulla oblongata. It 

 is situated behind the pyramid and olive, extending laterally as far as the inferior 

 peduncles, and dorsally to within a short distance of the rhomboid fossa. The 

 reticulum is caused by the intersection of bundles of fibers running at right angles 

 to each other, some being longitudinal, others more or less transverse in direction. 

 The formatio reticularis presents a different appearance in the anterior district from 

 what it does in the lateral; in the former, there is an almost entire absence of nerve 

 cells, and hence this part is known as the reticularis alba; whereas in the lateral 

 district nerve cells are numerous, and as a consequence it presents a gray appear- 

 ance, and is termed the reticularis grisea. 



In the substance of the formatio reticularis are two small nuclei of gray matter : 

 one, the inferior central nucleus (nucleus of Roller}, near the dorsal aspect of the hilus 

 of the inferior olivary nucleus; the other, the nucleus lateralis, between the olive 

 and the spinal tract of the trigeminal nerve. 



In the reticularis alba the longitudinal fibers form two well-defined fasciculi, 

 viz.: (1) the lemniscus, which lies close to the raphe, immediately behind the 

 fibers of the pyramid; and (2) the medial longitudinal fasciculus, which is continued 

 upward from the anterior and lateral proper fasciculi of the medulla spinalis, and, 



