INTERNAL STRUCTURE OF THE MESENCEPHALON. 587 



Inferior colliculus 



Mesencephalic root of 

 ' trigeminal nerve 



^/Nucleus of trochlear nerve 

 - Brachium inferius 



J\ Medial longitudinal 

 bundle 



Medial 

 lemniscus 



Brachia Conjunctiva. As the brachia conjunctiva leave the pons and sink 



into the tegmentum of 

 ithe mesencephalon, they 



undergo a complete de- 



cussation, subjacent to 

 i the inferior colliculi and 



the central gray matter 



(Figs. 520, 521, p. 587; 



and 522, p. 588). In this 



manner each brachium 



is transferred from one 



side, across the median 

 'plane, to the opposite 



side. The decussation 



is completed at the level 



of the superior borders 



of the inferior colliculi, 



and then each brachium 



proceeds upwards into 



the superior part of the 



tegmentum, where it en- 

 counters the red nucleus. 



Into this a large propor- 

 tion of its fibres plunge, 



and come to an end in 



connexion with the 



nuclear cells. Many of 



the fibres, however, are FJG 52 o. TRANSVERSE SECTION THROUGH THE HUMAN MESENCEPHALON 



carried around the nucleus AT THE LEVEL OF THE INFERIOR COLLICULUS. 



so as to form for it a 



iperior colliculus 



Basis 

 pedunculi 





Lateral geniculate ' 

 body~~ 



Inferior brachium 



Medial geniculate 

 body 



Medial lemniscus 



Basis pedunculi 



Optic tract 



Central gray matter 



Aqueduct 



Tegmentum 



Nucleus of oculomotor 

 nerve 



Medial longitudinal 

 bundle 



Red nucleus 



Fibres of brachium 

 conjunctivum 



Oculomotor nerve 

 Substantia nigra 



_ i-Corpus mamillare 



i. 521. TRANSVERSE SECTION THROUGH THE HUMAN MESENCEPHALON AT THE LEVEL OF THE 



SUPERIOR COLLICULUS. 



