198 



TOPOGRAPHICAL ANATOMY OF THE 



lies deep in the depression between the cerebellum and the corpora 

 quadrigeinina. 



The mid-brain (Mesencephalon).— The mid-brain is the short and 

 relatively narrow segment joining the pons and cerebellum on the one 

 hand with the cerebrum on the other. It has a dorsal part formed by 

 the corpora quadrigemina, and a larger ventral portion consisting of 

 the cerebral peduncles. Running through the mid-brain is a con- 

 stricted passage, the aquceduchis cerebri, which connects the third and 

 fourth ventricles. 



Brachium of posterior colliculus. \ 



Corpora quadrigemina (anterior colliculus). 



Corpora quadrigemina \ 

 (posterior colliculus). ^ 

 l\ 

 Brachium conjunctivum. 

 Brachitun pontis. 

 VIII. 

 Restiform bodv.^ 



Pineal body. 

 ■■ Brachium of anterior colliculus. 

 Lateral geniculate body. 

 j Cor])US callosum. 



i Optic tract. 



Facial tubercle. 



Pyramid. / 

 VIL 

 Corpus trapezoideum. 



Optic chiasma. 

 \ Tuber cinereum. 

 ^ Hypophysis. 

 Mammillary body. 



Medial geniculate body. 



Tractus transversus. 



III. 

 Cerebral peduncle. 



VI. ! 



Pons. 



Fig. 95. — Lateral aspect of the hind-brain and mid-brain, after removal of the 

 cerebellum. The Roman numerals apply to cerebral nerves. 



Corpora quadrigemina} — In the intact brain these bodies are 



completely hidden by the cerebral hemispheres, but at the present 



stage of the dissection they are revealed as four rounded elevations, 



arranged in pairs, between the thalami and the cerebellum. The 



anterior elevations (colliculi anteriores) are larger and more clearly 



defined, and are closer together than the posterior colliculi. The latter 



are separated from each other by a wide and shallow groove. The two 



colliculi of the same side are separated by a narrow but not very deep 



transverse groove. Laterally each colliculus ^ is continued by a 



' Corpus [L.], body. Quadri [L.], four + geminus [L.], twin. 



- Colliculus (dim. oi collis) [L.], a mound. 



