STRUCTURE OF MEDULLA OBLONGATA 



819 



mination of the afferent or sensory cranial nerves and of the sensory portions of the 

 mixed nerves correspond directly to the nuclei of the fasciculus gracilis and 

 fasciculus cuneatus, and to the cell-bodies of association and commissural neu- 

 rones of the medulla and cord and, functionally, are merely anterior continua- 

 tions of these. 



The nuclei of the efferent or motor cranial nerves lie in two parallel lines, one 

 near the mid-line and the other more laterally placed. The nuclei giving origin 

 to the oculomotor, the trochlear, the abducens, and the hypoglossus are near the 

 mid-line, and correspond to the ventro-medial and dorso-medial cell groups of the 

 ventral horns of the spinal cord; the nuclei of origin of the masticator (motor 



Figs. 



645 AND 646. — Diagrams showing the Composition op the Cerebellar Portions 

 OF the Internal and External Arcuate Fibres. 



Nucleus of 

 /asciculus cuneatus 



Nucleus of 

 fasciculus 

 gracilis 



Commissural nucleus 

 of ala cinerea 



Dorsal external arcuate fibres 



-.Restiform body 



Spinal tract of trigeminus - 



Ventral external arcuate fibers 



Nucleus of tractus solitarius 

 Nucleus of ala cinerea ,' Medial nucleus and descending root o£ 

 vestibular nerve 



Nucleus of fasciculus 

 cuneatus 

 ^Nucleus ambiguus 



_\ — Restiform body 



Root fiilum of vagus 

 ■" Cerebello-olivary fibres 



Ventral external arcuate fibres 



root of the trigeminus) of the facial, and the nucleus ambiguus giving origin to 

 the motor portions of the glosso-pharyngeal and vagus nerves, together with the 

 nucleus of the spinal accessory, correspond to the ventro-lateral and dorso-lateral 

 cell-groups of the ventral horns of the spinal cord. The nerve-roots having medial 

 nuclei of origin are those which make their exit from the brain-stem along the more 

 medial superficial Une, while those having the more lateral nuclei comprise the 

 more lateral line of roots apparent on the surface of the stem. Some of the effer- 

 ent fibres of the vagus, supposedly visceral efferent, arise from a small nucleus 

 dorso-medial to the nucleus ambiguus, the dorsal efferent nucleus of the vagus. 

 1 he first two pairs of cranial nerves, the olfactory and optic, are attached to the 



