362 JOHN WARREN 



as do the commissural fibers in mammalia. It is foi-med, how- 

 ever, as a distinct commissure only in Hphenodon and Lacertilia. 

 He thinks it more than probable that its fibers are represented in 

 amphibia by fibers which cross the roof of the diencephalon in 

 the superior commissure, 



Superior commissure 



The superior commissure is a very. constant tract in the ver- 

 tebrate brain and has a very definite position. It lies immediately 

 cephalad to the stalk of the epiphysis and below the pineal recess 

 in the upper and hinder part of the diencephalon. Osborn (78) 

 first gave it the name superior commissure and traced its homolo- 

 gies. He showed it in the brain of Menopoma, fig. 8. It was also 

 described at about the same time by Bellonci. Burkhardt (18) 

 described its homologies in lower vertebrates, reptiles and birds. 

 Cameron (15) gives an excellent account of this structure in tel- 

 eosts, amphibia, reptiles, birds and mammals. In teleosts the 

 tract appears early and he found fibers arising from the cells in 

 one ganglion habenula and passing to the other, while other fibers 

 passed to cells in the epiphysis of the same and also opposite 

 sides, forming a real decussation. 



In amphibia he studied the frog, toad and newt. In these 

 forms the commissure was found to lie some little distance cepha- 

 lad to the stalk of the epiphysis with quite an interval between. 

 He emphasizes this as an amphibian characteristic. This is not 

 always the case, as in Necturus, Warren (97), it lies close to the 

 stalk of the epiphysis. This is shown also by Osborn (78) in 

 Menopoma, fig. 8, Mrs. Gage (28), Diemyctylus, and Kupffer 

 (57), figs. 180, Salamandra, However Kupffer, fig. 228, Rana 

 esculenta, shows the condition described by Cameron. In Came- 

 ron's amphibian type, he finds that later a second set of fibers 

 appears in the anterior part of the commissure and does not enter 

 the ganglia habenulae. He was unable to follow their further 

 course. It is possible that these fibers may correspond to Elliot 

 Smith's commissura aberrans of reptilia which according to him 



