EDITORIAL 



The Cortical Optical Centre in Birds. 



The address which appears in synopsis elsewhere in this 

 number prompts us to call attention to the fact that the tract 

 described by Dr. Edinger is by no means the earliest connection 

 found between cerebrum and the optic centers. It does not 

 appear from the paper what part of the tectum is the terminus 

 of the " tractus occipito-tectalis " but it is obvious that it is a 

 direct associational tract. Even in fishes the writer has distin- 

 guished a strong tract entering the axial ( cerebral ) lobe from 

 diencephalic niduli and effecting connections with other regions. 

 Among these is a contingent springing from the geniculata of 

 either side where they arise in large " switch cells " one limb 

 of which seems to be connected with tectal tracts. Now, the 

 writer claimed several years ago that the axial lobe of fishes 

 must contain in potential the elements of the cortex and that 

 the elementary connections would all be discovered there. 

 Histological evidence was brought forward to show that 

 the axial lobe is by no means the simple homogene- 

 ous structure it had been supposed. // cannot be homo- 

 logous to the striatum. First, it contains a multitude of dis- 

 tinct niduli. Second, these niduli differ among themselves 

 in form, size, color reactions and processes. TJiird, the tracts 

 connecting these niduli pass in various directions. For example, 

 in the cephalic parts large cells give rise to axis-cylinders pass- 

 ing into the ventral peduncles. In the meso-caudal portion is 

 a cell cluster on either side which receives the lateral olfactory 

 radix in exactly the same way that the pyriform lobe of mam- 

 mals does and since a homologue of the descending fornix 

 springs from the same cell mass and passes to the mammillaries 

 (which positively occur in all fishes in the usual place and have 

 nothing to do with the hypoaria ) it seems necessary to consider 

 that the cell cluster contains the homologon of the hippocampus. 



