THE MIDBEAIN. 



123 



the whole system arises from a nucleus lying in the region of the Nucleus 

 fasciculi posterior. The author is unable to differentiate a separate nucleus. 

 The relation of the posterior longitudinal fascicitlus to the posterior com- 

 missure requires further elucidation. This has been retarded, because both 

 bundles are so difficult to bring to degeneration in continuo. 



Quite ventral in the anterior part of the midbrain-base lies a flat len- 

 ticular ganglion, which receives bundles, among which are some from the 

 Corp. striata of the cerebrum. So far as the author sees, it is best defined 

 in the reptiles and birds. The mammals have, in the same location, two 

 ■ganglia: one behind the other, the anterior one being called Corpus sub- 

 thalamicum, and the posterior Substantia nigra. Which one of these cor- 



f Outer and inner laminse of 

 1. opticus 



Gray matter of central canal 



/ Decussation of the deep medul- 

 X lary stratum 



. r Median portion of tile deep 

 (_ medullary stratum 



f Lateral portion of the 

 \ deep med. stratum 

 Posterior commissure 

 Fasc. long. post. 

 . Opticus 

 Nucl. prof. lat. 



- Nuel. prof. med. 

 — Gangl. ventr. tegmenti 



Mg. 73. — Frontal section through the midbrain of Lacerta. 



responds to the basal ganglion of lower vertebrates is yet uncertain, the 

 Tterm Ganglion ventrale tegmenti being used to designate the structure (see 

 Fig. 73). 



To the special ganglia of the thalamencephalon must be reckoned two 

 not clearly defined cell-aggregations: one lying in the lateral portion of 

 the base and one close beside the median line. Into both pass portions of 

 the deep medullary stratum: into the lateral one, the uncrossed fibers, and 

 into the median one the crossed fibers of the median portion of the deep 

 medullary stratum. The nuclei may be designated as the lateral and median 

 ■deep midhrain-nuclei (nuc. profund. lat. and nuc. profund. med., Fig. 73). 



The midbrain-base is naturally, in fishes, traversed also by those fibers 



