THE CRANIAL NERVES AND THEIR NUCLEI 



183 



Secondary Afferent Paths. From the cells of the main sensory and spinal 

 nuclei of the trigeminal nerve arise fibers which enter the reticular formation 

 and are there grouped into longitudinal bundles from which collaterals are given 

 off to the motor nuclei of the brain stem (Fig. 131). There are at least two such 

 longitudinal bundles in each lateral half of the brain. The ventral secondary 

 afferent path of the trigeminal nerve consists for the most part of crossed fibers 

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

 thalamic tract in the medulla, and dorsal to the medial lemniscus in the pons 



Mesencephalon \- 



Pons-\-- 



Ventral cochlear nucleus 



Medulla oblongata 



Cerebral aqueduct 



-/ Inferior colliculus 



Mesencephalic nucleus of N. V 



Sensory nucleus of N. V 

 -/^-Fourth ventricle 



Vestibular nucleus 



Dorsal cochlear nucleus 



-Nucleus of tractus solitarius 



Nucleus of spinal tract N. V 



Central canal 



*p& M 



Fig. 130. Sensory nuclei projected upon a median sagittal section of the human brain stem. 

 Horizontal lines, general somatic sensory nuclei; cross-hatching, visceral sensory nucleus; stipple, 

 special somatic sensory nuclei. 



and mesencephalon (Fig. 132). It is composed in large part of long fibers which 

 reach the thalamus. The dorsal secondary afferent path of the trigeminal nerve 

 consists chiefly of uncrossed fibers and lies not far from the floor of the fourth 

 ventricle and the central gray matter of the cerebral aqueduct. It consists in 

 considerable part of short fibers (CajaL 1911; Wallenberg, 1905; Economo, 

 1911; Dejerine, 1914). 



The proprioceptive nuclei of the cranial nerves are not well known. They 

 have to do with afferent impulses arising in the muscles of mastication and in 



