162 



THE NERVOUS SYSTEM 



The median longitudinal fasciculus is more conspicuous in the mesencephalon 

 than in other parts of the brain stem, but it occupies the same relative position, 

 that is, near the median plane close to the central gray matter. At the level of 

 the superior colliculus it forms a rather broad obliquely placed lamina, extending 

 dorsolaterally from the median raphe, which together with the corresponding 

 lamina of the opposite side produces in transverse sections a V-shaped figure 

 (Fig. 116). The apex of this V is directed ventrally; and included between its 

 two limbs are the oculomotor nuclei. At the level of the inferior colliculi the 



Stratum zonale 

 Stratum griseum 

 Stratum opticum 



Stratum Iemnisci'~r7 l 

 Stratum profundum-^ 

 Aqueduct of cere 



brum 

 Medial lemnis- 



Superior colliculus 



Nucleus of oculomotor nerve 

 Medial longitudinal fasciculus 

 Thalamo-olivary tract 



Inf. quadrigeminal brack. 

 Med. gen. body 



Dorsal tegmental decussation 



Ventral tegmental decussation 



Red nucleus 

 Oculomotor nerve 



gf Basis pedunciili 

 Substantia nigra 



Fig. 116. Section through the mesencephalon of a child at the level of the superior colliculus. 



Pal-Weigert method. (X 4.) 



medial longitudinal fasciculus lies immediately ventral to the nucleus of the 

 trochlear nerve (Fig. 114). In the pons the nucleus of the abducens nerve is 

 placed on its dorsolateral border. The close relation of this fascicle to the nuclei 

 for the motor nerves of the eye is of considerable significance, since according 

 to the law of neurobiotaxis (p. 179) it is an expression of the fact that the majority 

 of the afferent fibers to these nuclei come from this fascicle. This bundle of 

 fibers, the composition of which is discussed on pages 152 and 329, is a chief 

 factor in the reflex control of the movements of the eyes, and especially in the 

 coordination of these movements with those of the head and neck. 



