Kappers, Teleostean and Selachian Brain. 57 



In fact, Edinger has already mentioned that in the bony fishes 

 the medial part also goes to the base, but without adding that the 

 decussation of this part is separated from the so-called lateral 

 decussation (pars anterior) by the caudal fiber groups of the tr. 

 lobo-cerebellaris. 



But this does not exhaust the number of the lemniscus fibers. 

 A fourth very considerable group from the most caudal part of the 

 tectum runs through the posterior part of the colliculus and unites 

 with the first uncrossed part (Figs, li, lii), with which it runs in a 

 caudal direction at the lateral side of the mesencephalon. This 

 part also contains fibers from the colliculus. 



Accordingly, to recapitulate, the lemniscus consist of four parts 

 (Figs, xlviii to li) : 



(i) The most frontal part, arising directly behind the com. 

 posterior, continues to occupy a lateral position in the mesenceph- 

 alon and does not decussate. This contains only tectum fibers. 



(2) A part, which contains colliculus fibers, forms the pars 

 anterior of the com. ansulata (pars inferior of the higher verte- 

 brates), crossing between the frontal and the caudal parts of the 

 tr. lobo-cerebellaris. 



(3) ^ group which contains, besides tectum fibers, many fibers 

 from the colliculus decussates behind the most caudal bundle of 

 the tr. lobo-cerebellaris at the level of the most posterior attach- 

 ment of the lobi inferiores with the brain and forms the pars 

 posterior commissurce ansulatce (homologous with the pars superior 

 of amphibians and reptiles). 



(4) A part, also containing fibers from the colliculus, but going 

 without decussation, in a caudal direction together with the first 

 mentioned undecussated part. 



Accordingly, we find three lemniscus groups in the caudal part 

 of the mid-brain (Fig. lii) lying peripherally on both sides of the 

 median line. The part lying highest and most lateral contains 

 the undecussated fibers of the first and fourth groups, followed 

 more basally by the decussated third group, and finally close to 

 the median Ime, the second group, also decussated, the two tracts 

 separated only by the corpus interpedunculare. The fibers of 

 the lemniscus go caudad in these relations and end for the most 

 part in the medulla oblongata (and spinalis), and in smaller num- 

 bers enter the cerebellum, so that their further course will be 

 taken up under the metencephalon. 



