302 



ANATOJIY OF THE CENTRAL NERVOUS SYSTEM. 



amphibians and reptiles, one recognizes that these fibers, so far as they do 

 not pass into the fillet, belong to the midbrain itself and end in cells partly 

 on the same side and partly on the opposite side. At the corresponding 

 point in the hitman brain there are also groups of cells, the ganglion pro- 

 fundum mesencepJiali laterals et mediale. 



Scattered cells in the base of the midbrain probably give origin to a system of 

 fibers, very interesting phylogenetically. It will be recalled that in bony fishes at 

 this location there is a large ganglion, the Torns semicircularis, and that from it a 

 large bundle may be followed into the lateral tracts. Boyee has recently succeeded 

 in finding, in a cut through one side of the brain of a cat, a bundle which, begin- 

 ning in the base of the midbrain, may, through operatively induced degenerations. 



Fig. 195. — Fibers arising in the roof of the midbrain. Dorsally the Tractus 

 opticus, ventrally the deep medullary layer {Tiefcs 3J(iy];). Diagrammatic. 



be followed out of the midbrain as far downward as the anterior and lateral col- 

 umns of the spinal cord. 



In the central gray matter, below the qnadrigeminal bodies, appear the 

 first ganglion-cells which give rise to a cranial nerve: nervus oculo-motorius. 

 From their union, the nucleus nervi oculo-motorii, the root-fibers of the 

 nerve pass ventrally throu^gh the tegmentum and the crusta toward the base 

 of the brain, where they pass out imited into thick bundles (see Mg. 199). 

 The motor-oculi nerve contains fibers to several muscles within and about 

 the eye. Since nuclear paralysis of individual muscles of the group supplied 

 by this nerve has been observed, it is very probable that the nucleus con- 

 sists of a complex of small nuclei, somewhat separated from one another. 



