

THE MID-BRAIN OR MESENCEPHALON 



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face of each peduncle is crossed from the medial to the lateral side by the superior 

 cerebellar and posterior cerebral arteries; its lateral surface is in relation to the 

 gyrus hippocampi of the cerebral hemisphere and is crossed from behind forward 

 by the trochlear nerve. Close to the point of disappearance of the peduncle into 

 he cerebral hemisphere, the optic tract winds forward around its ventro-lateral 



Inferior colliculi 



Nucleus of oculomotor 

 nerve 



Lateral lemniscus 



Medial longitudinal 

 fasciculus 



Medial lemniscus 



Raphe 

 . Transverse section of mid-brain at level of inferior colliculi. 



surface. The medial surface of the peduncle forms the lateral boundary 

 of the interpeduncular fossa, and is marked by a longitudinal furrow, the oculo- 

 motor sulcus, from which the .roots of the oculomotor nerve emerge. On the lateral 

 surface of each peduncle there is^a second longitudinal furrow, termed the lateral 

 sulcus ; the fibers of the lateral 5pmniscus come to the surface in this sulcus, and 

 >ass backward and upwar^LjJwBsapptear under the inferior colliculus. 



Cerebral aqueduct 



Nucleus of oculomotor nerve 

 Medial longitudinal 

 fasciculus 





Fia. 712. Transverse section of mid-brain at level of superior colliculi. 



Structure of the Cerebral Peduncles (Figs. 711, 712). On transverse section, each 

 peduncle is seen to consist of a dorsal and a ventral part, separated by a deeply 

 pigmented lamina of gray substance, termed the substantia nigra. The dorsal part 

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