CuRRAN, A Neiv Association Fiber Tract. 649 



different places of termination. Moreover, the more distant the 

 areas nnited by these fibers, the deeper are they from the surface ; 

 and, conversely, the more superficial the fibers in the cortex are, the 

 closer are the areas they unite. In other words, the long associating 

 fibers lie deeply and the sort lie superficially. This is an important 

 and a helpful law; for it enables us, when we meet a tract lying 

 deeply, to say with tolerable certainty that it unites distant parts of 

 the cortex or distant nuclei. A tract is more easily dissected if fol- 

 lowed from the place where it appears as a separate bundle to its 

 distribution in the cortex. Owing to the tendency of fibers to form 

 into bundles in all long tracts there is a line of cleavage which, if 

 found and followed, assists us to overcome the intercrossing difii- 

 culty which appears as we approach the cortex from within. A dis- 

 section hard or even impossible to do when started from one point 

 will be easy when begun in another. If the difiiculty of finding the 

 right place in which to begin is appreciated, there will be less reason 

 for disappointment at any failure to get the best results in the 

 initial attempts. By considering for a moment the behavior of any 

 substance having longitudinal fibers, such as an ordinary board, 

 when subjected to the process of splitting we are able to glean some 

 information which assists us in splitting, or separating, the white 

 substance of the brain, which also has longitudinal fibers. If we 

 take a piece of board, the grain of which is straight, and make a 

 cut in the direction of the grain for a couple of inches along the 

 board, but close to the edge so that the strip will be narrow, and then 

 Avith our fingers separate the strip, we shall find that by the time 

 we have pulled it asunder for a couple of feet the strip is much nar- 

 rower than when Ave began, the split not having continued exactly 

 in the grain of the wood. If, on the other hand, Ave start the split 

 in the middle of the end of the board and then tear it asunder, Ave 

 shall find that the lx)ard is split in the grain of the A\^ood. Here the 

 resultant of the applied forces is acting in the right direction, and 

 there is no tendency, as in the former case of the small strip, for 

 one side to bend and the other to remain straight and thus alloAv 

 the bend to be continually breaking off fibers from the smaller until 

 the strip becomes narroAv, and, if Ave proceed far enough, tapers out 



