The origin of the Corpus Callosum, a contrib. upou the Cerebral Comm. etc. 233 



Descriptive Part. 

 Teleosts '. 



The interlobular commissures in the Teleosts traverse different 

 portions of the ridge which connects the cerebral lobes. This ridge 

 lies in the ventriculus communis and, in the Cyprinidae (Cyprina 

 carpio), extends to about 72 t^^G height of the cerebral lobes, and 

 lies opposite the boundary of the hemispheres and thalami (fig. 3). 

 As observed by Kabl-Rückiiaed we do not find any line of demar- 

 cation between the olfactory and cerebral h)bes. The olfactory nerves 

 arise from the antero- internal angle of the hemispheres, and in the 

 carp's brain, this region (olf. fig. 2), is fairly well defined as the ol- 

 factory centre by its fibre tracts and by a differentiation in the cha- 

 racter of the cells. The olfactory lobes are not well defined from the 

 hemispheres. The entire ridge between the hemispheres is largely 

 composed of fine transverse fibres. Among these we may distinguish 

 six distinct tracts. Two of these tracts may be considered together 

 as unmistakeably associated with the olfactory lobes; a third may 

 be doubtfully added to this group. The remaining three seem to 

 form a commissural group of the hemispheres proper. 



I. Commissural fibres of the hemispheres. These are 

 divided into three bundles. The lowest cm' (fig. 1) is the smallest 

 and the least defined and in carmine preparations it can only be 

 clearly seen in transverse sections. Unlike the other bundles it lies 

 beneath the cerebral peduncles. Its delicate fibres pass upwards and 



* Note upon the Methods pursued. My principal object was to 

 procure continuous series of sections in three planes, horizontal, transverse 

 and sagittal. The brains were hardened in Müllers fluid, placed in running 

 water and gradually transferred to OuOg Alcohol, through weaker grades. 

 Staining was in to to by immersion from 7 to 10 days in Ammonia carmine. 

 Imbedding in Paraflin by the chloroform process for the small brains, and clove 

 oil, turpentine, for the large brains. Using Jung's Microtome, the largest size 

 is preferable. The series wore adhered to the slide by Mayek's admirable me- 

 thod. I believe that the results obtained by the Ammonia carmine staining, 

 while perhaps less brilliant than those obtained by other Methods , are more 

 reliable. My earlier preparations of tlie Amphibian brain were after Caluek- 

 la's method of imbedding in an egg mass and cutting in spirit. This mass 

 however sometimes diminishes the brilliancy of the staining by chemical action- 

 The paraffin method requires, in brain sections, more skill and practice, but 

 when once acquired, faultless section series of '/70 mm in thickness and 12 nun 

 surface measurement may be cut in ribbons and prepared very rapidly. 



