THE COMMISSURES. 247 



these parts with two, and even more, neighboring sensory centers. The 

 speech-centers appear, as a whole, to lie in the common boundary region of 

 the sensory and association centers. 



One sees that even the short description, which the author was able to . 

 give here, of the tracts running in the white medullary substance shows this 

 to be a very complicated structure. In fact, sections made at any place 

 whatsoever, never, or almost never, show one of the systems alone; at least, 

 decussating fibers are almost always present, originating from the associa- 

 tion-bundles, or from the corpus callosum also, or from the other systems of 

 commissures. Perhaps the collaterals, the exit of which from the fibers of 

 the corona radiata is easily demonstrable in the mouse by means of the 

 G-olgi method, here play an important role in complicating matters. How- 

 ever, one recognizes even now the cardinal feature of brain-structure when 

 one sees that from particular cortical areas definite fasciculi pass to definite 

 termini. 



Numerous investigators have turned their attention to the histology of the 

 cerebral cortex and the finer anatomical relations of its structure. Hitherto the more 

 it was investigated, the more difficult the solution of the problem appeared to be. 

 New and more complicated relations were constantly becoming known. BaiUtirger, 

 Bevan Lewis, Clarke, Meynert, Golgi, Bellonci, S. Ramdn y Gajal, Kolliker, and many 

 others have attempted to throw light upon the most important points. The cortex 

 of the cornu Ammonis was specially investigated by Meynert, Kolliker, Henle, Duval, 

 Schaffer, Golgi, Sola, and Ramdn y Gajal. Much was learned concerning the sys- 

 tem of fibers in the white matter of the hemisphere by F. Arnold, Reil, and Bur- 

 dach, even by means of the teasing method, while the microscopic investigations by 

 Meynert, Sachs, Brissaud, and Dijerine, more particularly the embryological studies 

 of Flechsig, and the numerous experimental researches of Gudden, Lmcenthal, Mona- 

 Icow, and others, have advanced our knowledge of the subject wonderfully. The 

 advantages that have accrued to the study of the anatomy of this portion of the 

 brain from investigations on pathological brains are not to be undervalued. Wernicke, 

 Charcot, Fir6, Pitres, Friedmann, SioU, Monakow, Richter, Zacher, Dij^rine and 

 others have made such investigations. 



