200 JOURNAL OF COMPARATIVE NEUROLOGY. 
the injury is of special interest. Had the sectioned fibers of 
the callosum merely degenerated in the part distal to the 
lesion, there would have been a considerable number of fibers 
in the corpus callosum on each side of the injury, instead of an 
entire absence of them on the lateral side. Their absence 
on one side and presence on the other can be under- 
stood by supposing that the fibers cut near their cells of 
origin—fibers whose cells were situated in the injured hemis- 
phere—degenerated throughout their whole extent, while 
fibers cut at a greater distance from their cells of origin— 
fibers whose cells were situated in the opposite hemisphere— 
degenerated upon the distal side of the lesion only. In von 
GuDDEN’s Gesammelte Abhandlungen (34) there is recorded a - 
similar observation. Six or eight weeks after removal of one 
cerebral hemisphere in a young rabbit, he found that the ante- 
rior commissure and corpus callosum had completely atrophied 
in the remaining hemisphere. 
In the upper region of the cortex the wound is recognized 
with difficulty, because there is so little scar tissue and the 
number of crossing fibers is so great. It can, however, be 
seen as a faint line along the path the knife must have taken to. 
reach the underlying parts where the injury is more apparent. 
Fig. 6 is a camera lucida tracing of some of the fibers in the 
scar. It was taken from the same preparation as Fig. 3 about 
one-third the way up from the corpus callosum to the cortex. 
Two fibers fulfil the requirement of passing into the brain 
tissue on each side, and the others would probably do so if 
they could be followed far enough. 
Rat No. 4 was twelve hours old at the time of the opera- 
tion and forty days old when killed. The meninges were quite 
normal, and there was no sign of the injury apparent on the 
surface of the brain. Serial sections revealed a lesion extend- 
ing 1 mm. behind the posterior extremity of the splenium and 
almost 14 mm. in front of that point. The general appearance 
of the wound is shown in Fig. 4. The upper part of the 
cortex is normal, no scar tissue can be seen there, and nerve 
fibers have a normal distribution. In the lower half is a trian- 
