THE SUBTHALAMIC REGION, ETC. 



115 



sides. In human beings we find groups of cells at points cor- 

 responding to these terminal cells of birds, fishes, etc. (lateral 

 and median ganglion, Fig. 66). 



In the central gray matter, under the corpora quadrigemina, 

 we first meet with ganglion-cells which give origin to a cranial 

 nerve, the oculomotor. From their union, which forms the 

 oculo-motor nucleus, the roots of that nerve pass ventrad 

 through the tegmentum and the crusta to the anterior surface 

 of the brain, and emerge in thick bundles. (See Fig. 72.) The 



FIG. 66. 



The fibres arising in the raid-brain roof. Dorsad the optic tract, ventrad the deep 

 marrow. The diagram also shows the other optic roots. 



oculo-motor nerve contains fibres to several internal and external 

 muscles of the eye. From the fact that nuclear paralyses of 

 single muscles from the group supplied by this nerve have been 

 observed, it is probable that this nucleus consists of a complex 

 of small nuclei somewhat separated from each other. In human 

 beings, indeed, a distinct demarcation can be made out in several 

 parts. Far forward, lying partly in the lateral wall of the third 

 ventricle on each side, is a small nucleus, the nucleus anterior. 

 It sends a few fibres caudad to the main portion of the nerve. 

 Behind it lies the nucleus posterior. It extends the whole 



