38 



THE NERVOUS SYSTEM 



of that nerve; and after crossing the raphe they run in two tracts to the ventral 

 part of the lateral nucleus of the thalamus. The ventral secondary afferent 

 path is located in the ventral part of the reticular formation, close to the spino- 

 thalamic tract in the medulla oblongata and dorsal to the medial lemniscus in 

 the pons and mesencephalon (Figs. 132, 234). The dorsal tract lies not far 

 from the floor of the fourth ventricle and the central gray matter of the cerebral 



'Medial lemniscus 

 Mesencephalon 



o'o^ 1 *~o j- Medial lemniscus 



Pons 



Dorsal secondary tract N. V 

 Ventral secondary tract, N. V 



^- Main sensory nucleus N. V 

 Pons 



N. V 

 -- Spinal tract N. V 



Spinal nucleus N. V 



Medulla oblongata 

 Fig. 232. Diagram of the exteroceptive pathways associated with the trigeminal nerve. 



aqueduct. It consists in considerable part of uncrossed fibers and of fibers hav- 

 ing a short course (Wallenberg, 1905; Economo, 1911; Dejerine, 1914). 



Neuron III. The afferent impulses are relayed from the thalamus to the 

 cortex of the posterior central gyrus by fibers of the third order, which run through 

 the posterior limb of the internal capsule. Their cells of origin are located in 

 the lateral nucleus of the thalamus. 



