284 



ANATOMY OF THE CENTRAL NERTOUS SYSTEM. 



peduncle. It arises from the niicleus ruber tegmenti, which lies in the teg- 

 mentum beneath the thalamus and the corpora quadrigemina. 



We distinguish anterior and posterior corpora quadrigemina, but this- 

 distinction is easy to the naked eye in many mammals alone. In all other 





Zrjzt.^ ''. 



Mtticlki 



flinlcn'tir, 





.Ya.J.. 



'^pvf.\\\a\\ 



Fig. 182. — The brain-struetures from the thalamus to the spinal cord (the 

 "brain-stem"). The cerebellum divided, and removed on the left. Bindearm, 

 Peduncle. Hinterhirn, Hiudbrain. Hirnschenkel, Crua Cerebri. KleinMrn, Cere- 

 bellum. MittelMrn, Midbrain. NaoMirn, After-brain. Riickenmark, Spinal cord. 

 Zwischenhirn, Interbrain. 



vertebrates the anterior are so large that the posterior corpora quadrigemina 

 disappear as small ganglia in the region under them. From the anterior 

 corpora quadrigemina arises a part of the optic nerves. The anterior cor- 



