100 



nerv3-t'ibres smerging frotn the general bunils and tenoiaating 

 in arborizations nenr the bodies of the nerve-cell^. Pig.'i?, 

 ar. , represents t*»o such arborizations near the same cell. 

 The character of the teruination is exceeiingly interesting. 

 The axones are founJ to present a reticalo-vesicular structure 

 throughout their whole length, the protoplasm apparently con- 

 sisting of vesicles of several degrees of size united by a 

 reticulum. No^ as the axone approaches its ternination, the 

 reticulation becomes naore pronounced, and tne final arboriza- 

 tion is seen to be essentially an expansion of the same thing. 

 The ending is simply a widely-spread, digitate reticulum. There 

 are many thorn-like branches frox all of the strands, and nu- 

 meroiis anastomoses occur tetfleen the principal ones. Consult 

 H'ig.57,ar. 



The remarkable group of nerve-cells comprising the roof- 

 nucleus has been variously interpreted, but its true relations 

 were not discovered until quite recently, ftohon ('77) first 

 described this collection of cells as the iaohkeme, a name 

 applied, of course, from the position occupied by its paired 

 members in the roof of the aqueduct of Sylvius. It was later 

 recognized in the brains of various fishes, Burckhardt ( '9?) 

 identifying it as the midbrain trigeminal nucleus. It has 

 remained for Sargent (1900) to show that not only is the roof- 

 nucleus present in all vertebrates, but that it is part of a 

 most interesting mechanism, the fibre of fteissner ('*^0). 

 Reissner's fibre is a rod-like body lying in the central canal 



