530 THE BRAIN OF MAMMALS, BY TH. MEYNERT. 



To it belongs the greatest proportion of the areas of the 

 pyramids, as seen in transverse section, which are about 

 to pass across the median line by broad decussating fasciculi 

 (fig. 261, D), and to enter the lateral column of the opposite 

 side. This passage of the pyramids into the lateral column 

 occurs, as Clarke and Lenhossek have stated, without inter- 

 ruption of the fasciculi by grey matter. The fasciculi of the 

 lateral column, which likewise pursuing a transverse course 

 first emerge from the decussation of the pyramid, interlace 

 with the fine transverse sectional areas of other already 

 descending fasciculi of the lateral column as a formatio 

 reticularis which first disappears in the uppermost portion 

 of the cervical region of the spinal cord (Stilling, Clarke, and 

 Deiters). 



This formatio reticularis moreover includes, in deep-lying 

 sectional planes, numerous large nerve corpuscles, which, how- 

 ever, as Stilling, Lenhossek, and Clarke have pointed out, are 

 only cells of origin of the accessory nerve. The formatio 

 reticularis in Man, however, apparently does not contain, as 

 Deiters maintains, such an accumulation of grey matter as is 

 adequate for the termination of so large a formation as that of 

 the inferior decussating fasciculi of the pyramids. It must be 

 conceded to Deiters that the decussation of the pyramids of 

 Mammals, to which he refers as furnishing more striking 

 evidence in favour of his explanation, exhibits far more 

 the appearance of sufficiency of grey substance in the plexi- 

 form formation, for the interruption of all the fibres of the. 

 pyramids, than in Man. But the fact that, with very small 

 pyramids, more grey matter can be observed in the medulla 

 oblongata of Mammals, than is present in Man, with his strong 

 pyramids, demonstrates that the two formations are not mutu- 

 ally related. It is rather the considerable development of grey 

 connective substance at this point, by which the brain of 

 Mammals generally is distinguished from that of Man, that 

 really produces the appearances in the medulla oblongata of 

 the Calf and of the Cat which favour the view of Deiters. 



The diminution in calibre of the far finer fibres of the 

 pyramids, as compared with the sections of those of the lateral 

 columns of the spinal cord, which favours the view of Deiters, 



