142 



THE NERVOUS SYSTEM 



peduncle. The two accessory olives are plates of gray substance, which in trans- 

 verse section appear as rods. The medial accessory olivary nucleus is placed be- 

 tween the hilus of the inferior olive and the medial lemniscus, while the dorsal 

 accessory olivary nucleus is located close to the dorsal aspect of the chief nuclear 

 mass. 



Structure and Connections. The gray lamina of the inferior olivary nucleus 

 consists of neuroglia and many rounded nerve-cells beset with numerous short, 

 frequently branching dendrites, the axons of which run through the white core 

 of the nucleus and out at the hilus as olivocerebellar fibers (Fig. 102) . About 

 these cells there ramify the end branches of several varieties of afferent fibers, 

 the origin of which is not well understood. Some come from a tract, designated 



Fourth ventricle 

 Principal vestibular nucleus 

 Spinal vestibular nucleus 

 Nucleus intercalate 



Restiform body 

 Spinal tract and 

 nucleus N. V 

 Ponlobulbar body 



Glossopharyngeal nerve 



Nucleus ambiguus 



Ventral spinocerebellar tract 

 Dorsal accessory olivary 

 nucleus 



Hilus of olivary nucleus 

 Inferior olivary nucleus 



Medial accessory olivary nucleus 



Ventral external arcuate fibers 



Tcenia of fourth ventricle 



Nucleus of hypoglossal nerve 



Dorsal motor nucleus of vagus 

 Tractus solitarius and 

 nucleus 

 Medial longitudinal 



fasciculus 

 Reticular substance 

 Olivocerebellar fibers 

 Vagus nerve 



Lateral reticular nucleus 

 Thalamo-olivary tract 

 Inferior olivary nucleus 

 Medial lemniscus 

 Hypoglossal nerve 

 Pyramid, corticospinal tract 

 Arcuate nucleus 



Fig. 103. Section through the medulla oblongata of a child at the level of the restiform body. 



Pal-Weigert method. (X4.) 



as the thalamo-olivary fasciculus; but it is not certain that they have their 

 origin in the thalamus; quite possibly they come from some other gray mass 

 in that neighborhood. Another group of fibers, consisting chiefly of collaterals, 

 comes from the ventral funiculus of the spinal cord and may be regarded as 

 ascending sensory fibers (Cajal, 1909). These belong to the so-called spino- 

 olivary fasciculus. 



Olivocerebellar Fibers. The axons from the cells of the inferior olivary 

 nucleus stream out of the hilus, cross the median plane, and either pass through 

 or around the opposite nucleus. Here they are joined by some uncrossed fibers 

 from the olivary nucleus of the same side. Thence they curve dorsally toward 

 the restiform body, passing through the spinal tract of the trigeminal nerve 



