NUCLEI OF CRANIAL NERVES 



821 



with the axones given by the cells of its nucleus, is beheved to extend as far downward as the 

 level of the fourth cervical segment of the spinal cord. This being in the level of origin of 

 the phrenic nerve, the tract forms a link in the respiratory apparatus which aids in the co- 

 ordinated respiratory movements. The axones given off by the cells of the nucleus of the 

 ala cinerea (terminal nuclei of the vagus and glosso-pharyngeus) course on both sides of the 



Fig. 647. — Scheme showing the RELAxrvE Size and Position of the Nuclei of Origin 

 (Red) of the Motor and the Nuclei of Termination (Blue) op the Sensory 

 Cranial Nerves. 



Nucleus of olfactory nerve 



Nucleus of oculomotor nerve ^ 



Nucleus of trochlear nerve ' 



Nucleus of mesencephalic root of 



masticator 



Chief motoi- nucleus of 



masticator 



Nuclei of optic 

 nerve 



Nucleus of facial'* 

 Nucleus of abducens'' 



Nucleus ambiguus (vagus and 

 glosso-pharyngeus) 



Nucleus of hypoglossus '' 



Pulvinar of 

 \ thalamus 

 Lateral genic- 

 ulate body 

 Nucleus of supe- 

 rior colliculus J 

 - Sensory nucleus of trigeminus 



, Nucleus of vestibular nerve 



Ventral nucleus of 

 cochlear nerve 



~ Dorsal nucleus of cochlear nerve 



•~ Nucleus alae cinereas (vagus and 

 glosso-pharyngeus) 



Solitary tract (vagus and glosso- 

 pharyngeus) 



" * Nucleus of spinal tract of trigeminus 



Nucleus of spinal accessory nerve , - 



mid-Une, associating nuclei of other cranial nerves with vagus and glosso-pharyngeal impulses, 

 many decussating to be distributed to the structures of the opposite side. Many join the lemnis- 

 cus of the opposite side and pass into the cerebrum; others are distributed to the motor neu- 

 rones of the cervical cord of the same and opposite sides (reflex axones), and no doubt 

 others form central connections with the cells of the reticular formation of the medulla, 

 though their precise relations have not been determined. < 



