144 



THE NERVOUS SYSTEM 



The dorsal spinocerebellar tract can readily be traced in serial sections of 

 the medulla because the large, heavily myelinated fibers of which it is composed 

 cause it to be deeply stained by the Weigert technic. It can be followed from 

 the spinal cord along the periphery of the medulla oblongata near the posterior 

 lateral sulcus. At first it lies ventral to the spinal tract of the trigeminal nerve 

 (Figs. 98, 99). But at the level of the lower part of the olive it inclines dorsally, 

 passing over the surface of the spinal tract of this nerve to reach the restiform 

 body (Fig. 101). Between this tract and the olive we find the ventral spino- 

 cerebellar tract also in a superficial position. 



The spinal tract of the trigeminal nerve is formed by the descending branches 

 of the sensory fibers of that nerve. They give off collateral and terminal 

 branches to a column of gray matter, resembling the substantia gelatinosa 



Tractus solitarius and nucleus 



Dorsal motor nucleus of vagus 



Nucleus of hypoglossal nerve 



Nucleus amblguus 



Medial longitudinal fasciculus 



Tectospinal tract 



Dorsal accessory olivary nucleus 



Medial lemniscus 



Medial accessory olivary nucleus 



Corticospinal tract 



Fig. 105. Diagram showing the location of the nuclei 



at the level of the 



' Vestibular nudeus 

 .--Nucleus cuneatus 



of the spinal tract N. V 



'" Dorsal spinocerebellar tract 

 -- Spinal tract N. V 

 Vagus nerve 



spinocerebellar tract 

 " Spinothalamic tract 

 Thalamo-olivary tract 

 -Inferior olivary nucleus 



Hypoglossal nerve 



and fiber tracts of the medulla oblongata 

 olive. 



Rolandi, with which it is directly continuous, and designated as the nucleus 

 of the spinal tract of the trigeminal nerve (Figs. 92, 98, 99, 101, 103). The tract 

 lies along the lateral side of the nucleus and is superficial except in so far as it 

 is covered by the external arcuate fibers, the dorsal spinocerebellar tract, and the 

 restiform body. It forms an elongated elevation, the tuberculum cinereum on 

 the surface of the medulla oblongata (Fig. 88). 



The formatio reticularis fills the interspaces among the larger fiber tracts 

 and nuclei. It is composed of small islands of gray matter, separated by' fine 

 bundles of nerve-fibers which run in every direction, but which are for the 

 most part either longitudinal or transverse. It is subdivided into two parts. 

 The formatio reticularis alba is located dorsal to the pyramid and medial to the 

 root filaments of the hypoglossal nerve and is composed in large part of longi- 



