172 



THE NERVOUS SYSTEM 



The fibers from the medial nucleus enter both right and left nerves. Some 

 from the caudal portion of the dorsal division of the lateral nucleus cross the 

 median plane. The others remain uncrossed. After sweeping in broad curves 

 through the tegmentum and red nucleus the fibers emerge through the oculo- 

 motor sulcus. All of the extrinsic muscles of the eye except the lateral rectus 

 and superior oblique are supplied by the medial and lateral groups of cells just 



described. 



t , Nucleus of Edinger-Westphal 



,. Nucleus of oculomotor nerve 



--Corpora quadrigemina 



Cerebral aqueduct 

 -Nucleus of trochlear nerve 

 Trochlear nerve 

 'Anterior medullary velum 



'Motor nucleus N. V 



. - 'Nticleus of facial nerve 

 , - Fourth ventricle 

 Nucleus of abducens nerve 



Mesencephalon 

 Oculomotor nerve 



Pans 

 Portia minor N. V- 



Facial nerve 



Abducens nerve- - ' 



Medulla oblongata- 



- Nuc. salivatorius superior 



- Nuc. salivatorius inferior 



Nucleus of hypoglossal nerve 



- - Dorsal motor nucleus N. X 

 .--Central canal 



Nucleus ambiguus 



Fig. 122. Motor nuclei of the cranial nerves projected on a median sagittal section of the 

 human brain stem. Circles indicate somatic efferent nuclei; small dots, general visceral efferent 

 nuclei; large dots, special visceral efferent nuclei. 



As one might expect from the fact that the oculomotor nerve supplies several distinct 

 muscles, its nucleus seems to be made up of a number of more or less distinct groups of cells; 

 but the efforts to locate subordinate nuclei have given rise to contradictory results. The 

 most significant work in this field has been done by Bernheimer (1904), who extirpated in- 

 dividual eye muscles in monkeys and studied the resultant changes in the cells of the oculo- 

 motor nuclei. According to him, the various muscles are supplied by the lateral nucleus in 

 the following order, beginning at the rostral end: levator palpebrae superioris, rectus supe- 

 rior, rectus medialis, obliquus inferior, and rectus inferior. Bernheimer says that the fibers 

 for the rectus inferior are entirely crossed, those for the obliquus inferior are in greater part 

 crossed, those for the rectus medialis for the most part uncrossed, those for the rectus superior 

 and levator palpebrse superioris entirely uncrossed. 



