278 C. JUDSON HEREICK 



related respectively wdth the colliculus inferior in general and 

 the nucleus posterior tecti. 



This system as a whole I compare provisionally \^^th the mammalian 

 commissure of Giidden; but if this comparison holds, it is evident that 

 the homology is only partial. The commissure of Gudden (commis- 

 sura arcuata transversa of Hannover, decussatio supraoptica ventrahs 

 of Edinger, '11, p. 346) seems to be a very complex system which has 

 been only incompletely analyzed. Sterzi ('15, p. 660) recognizes 

 five components: (1) a commissure between the medial geniculate 

 bodies, (2) a commissure between the inferior colliculi, (3) a decus- 

 sation between the medial geniculate body and the opposite globus 

 palhdus, (4) a decussation between the medial geniculate body and 

 the opposite temporal cortex, (5) fibers connected with the nucleus 

 subthalamicus. The only regions here enumerated which can be 

 recognized in Necturus are the inferior colliculus and tj^e subthalamus 

 (pars ventralis thalami). The mammalian connections of Gudden's 

 commissure with the two parts last mentioned may, however, be 

 represented in our tractus tecto-thalamicus et hypothalamicus cruciatus. 



In fishes, where the postoptic commissure complex is very highly 

 differentiated, the corresponding connection is in many cases very 

 clearly seen. This is the ^om.missura transversa of Haller. Victor 

 Franz ('12, p. 433) describes this tract in Gadus as comprising a true 

 commjissural connection between the torus semicircularis of the two 

 sides (the teleostean colliculus inferior), a decussation between the 

 torus and the opposite hypothalamus, and associated with the last 

 an uncrossed tract between the torus and the hypothalamus. This 

 is essentially similar to my findings in Necturus. I have confirmed 

 Franz' description of this commissure by personal observations on 

 Gadus and some other teleosts. The tractus tecto-lobaris of Acipen- 

 ser, as described by Johnston ('01, p. 71), contains similar elements, 

 although the uncrossed fibers are much more numerous and the num- 

 ber of fibers decussating in the postoptic commissure is very small. 

 Here most of the crossed fibers for the hypothalamus decussate in 

 the ventral commissure of the midbrain instead of in the postoptic 

 commissure. Many other variations of these relations are found in 

 different species of fishes, but in all cases there seems to be a connec- 

 tion between the equivalent of the colhculus inferior and the hypo- 

 thalamus associated with the postoptic commissure. It is possible 

 that the commissiua minor of C. L. Herrick ('92. p. 37 — ^the comnis- 

 sura Herricki of Edinger, Goldstein and Kappers) is the teleostean 

 representative of the myelinated fibers of the pars anterior of this 

 complex which in Necturus are related to the optic part of the tectum ; 

 for Kappers ('06, p. 28) has traced this commissure in Gadus to the 

 superficial layer of the most rostral end of the tectum opticum. The 

 teleostean commissura horizontalis of Fritsch, which reaches the 

 rostral border of the tectum opticum, may also correspond in part 

 with the amphibian pars anterior. 



