The Brai?i of Diemydylus Viridescens 291 



the long plexus between the portae and conarium would be- 

 long to the prosencephal. The relations of the plexuses in 

 man as shown by Wilder (55, Figs. 4743, 47 11) are very dif- 

 ferent from those found in amphibia, unless some new light 

 shall be thrown upon them by the study of sections by the 

 microscope. Upon such a study must depend the determina- 

 tion of the homologies of the plexuses and consequently 

 the dorsal limit between the segments. 



The cells of the paraphysis of diemyctylus are cubical and 

 not flattened as over the plexuses. Jefiries Wyman (59) ac- 

 curately described and figured cells in the frog, which were 

 taken from the midst of the vascular mass (supraplexus) and 

 surmised that they were part of the brain wall proper. This 

 is the earliest reference which I have found to this structure 

 (the paraphysis) but it has been overlooked in the extensive 

 bibliographies upon the epiphysis and paraphysis in which the 

 discovery has been assigned to much later investigators. 



The original use of this organ has been by some considered 

 as an eye (19) by others (45) as an auditory organ. Another 

 surmise may be ventured. From its origin in the embryo be- 

 fore the plexuses are formed, in a region, which by later 

 growth as shown by its extensive vascular supply, has need of 

 a means of repairing waste ; from the character of the one 

 layered endyma in the amphibia, it is suggested that it is con- 

 nected, at least in early stages, with the nourishment of the 

 brain. 



SULCI. 



In the mentencephal of human embryos, His (26) has very 

 carefully worked out the relation of the origin of nerve roots to 

 certain folds in the brain wall which become the center of cell 

 proliferation. These arise at a margin between the solid and 

 membranous portion of the wall (see Fig. 86, 92, which show 

 such folds at the origin of the 9th and 7th nerves), and may be 

 gradually overgrown by a new fold ; thus pushed together, 

 they may coalesce and apparently disappear as true folds. (See 

 wing of cinerea with which the loth is connected in Fig. 86). 

 These folds he calls Raute7ilippen. The relation of such folds 

 with nerve roots is clearly shown by Goronowitsch (21) in 



