524 



THE ORGANS 



terra crura cerebri or cerebral peduncles is loosely used lo include all except 

 the roof of the brain at this level, i.e., tegmentum and basis pedunculi. 



Efferent Peripheral Neurones. — The nucleus of nerve III or oculomotor nucleus 

 is located in the ventral part of the central gray in a V-shaped trough formed by 

 the fibres of the medial longitudinal fasciculus. The nucleus is divided into large 

 and small-celled groups. The large-celled groups are two lateral groups subdivided 



^issura ^(fr ^.. 



Fig. 354. — The region of the aqua;ductus Sylvii seen from above. Schema 

 showing the position of the nuclei of nerves III and IV and their subdivisions. (Edinger.) 

 I. The small-celled nucleus (here represented as one on each side) a, its ciliary, ^, its 

 pupillary portion. 2, The portion of the large-celled nucleus sending uncrossed fibres 

 to M. levator palpebras; 3, portion sending uncrossed fibres to M. rectus superior; 4 

 and 5, portions sending crossed and uncrossed fibres to Mm. rectus internus and 

 obliquus inferior; 6, portion sending crossed fibres to M. rectus inferior. The nucleus 

 trochlearis sends crossed fibres to M. obliquus superior. 



into anterior and posterior dorso-lateral and anterior and posterior ventro-mesial, 

 and a central or median group — nine in all. Between the cephalic or anterior 

 groups are on each side a small-celled group known as the Edinger-Westphal 

 nucleus, and still further forward are two small-celled anterior median nuclei. 

 The connections of these groups with the extrinsic muscles of the eye innervated 

 by nerve III (internal, superior and inferior recti, and inferior oblique) and the 

 levator palpebrae superioris and intrinsic eye muscles (ciliary and sphincter 



