140 



THE NERVOUS SYSTEM 



uli and perhaps also from these funiculi themselves a group of dorsal external 

 arcuate fibers make their way to the restiform body along the dorsal surface of 

 the medulla (Fig. 101). According to Cajal these fibers are well developed in 

 man, but absent in the cat and rabbit. The ventral external arcuate fibers are 

 said to include a certain number which arise in the lateral reticular and arcuate 

 nuclei and run dorsolaterally over the surface of the medulla to reach the 

 cerebellum by way of the restifrom body (Fig. 104). The arcuate nuclei are 

 small irregular patches of gray matter situated on the ventromedial aspect of 

 the pyramid and continuous rostrally with the nuclei pontis, with which they 



Spinal vestibular 

 nucleus 



Dorsal external 

 arcuate fibers 



Tractus solitarius 

 and nucleus 



Nucleus of 

 hypoglossal nerve 



Internal arcuate 

 fibers 



Dorsal spinocere- 

 bellar tract 



Medial longitudinal 

 fasciculus 



Ventral spinocere- 

 bellar tract 



Tectospinal tract 

 Medial lemniscus 



Inferior olivary 

 nucleus 



Hilus of olivary 

 nucleus 



Pyramid, cor ti co- 

 spinal tract 



Fig. 101. Section through the medulla oblongata of a child at 



method. (X 6.) 



Dorsal motor 

 nucleus of vagus 



Nucleus cuneatus 

 Restiform body 



Spinal tract and 

 nucleus N. V 



Nucleus ambiguus 



Reticular substance 



Lateral reticular 

 nucleus 



edial accessory 

 olivary nucleus 

 nferior olivary 

 nucleus 



Hypoglossal nerve 



Ventral external 

 arcuate fibers 



the level of the olive. Pal-Weigert 



seem to be homologous (Figs. 101, 103). They probably receive fibers from the 

 cerebral cortex by way of the pyramidal tracts; and, if so, the external arcuate 

 fibers which arise from them are homologous with the transverse fibers of the 

 pons. 



Although the facts stated above are pretty well established, only a small part of the 

 ventral external arcuate fibers are thus accounted for. The origin and course of the majority 

 of these fibers is still obscure. According to Cajal (1909) they arise from the nuclei of the 

 posterior funiculus, curve ventrally and medially over the surface of the medulla oblongata, 

 penetrate the pyramids or the anterior median fissure, cross in the median raphe, and join 

 the medial lemniscus of the opposite side. On the other hand, Edinger (1911) gives to 



