198 JOURNAL OF COMPARATIVE NEUROLOGY. 
into the degenerated areas. But a fiber such as is illustrated in 
the tracing, crossing the wound near its center and making 
connections with the brain tissue on both sides of the scar, 
must without doubt be new-formed. 
Rat No. 2 was operated on when seven days old and 
killed forty-two days later. The wound in the skull was indi- 
cated only by a slight roughness, ossification at this point being 
as complete as elsewhere. The dura mater was normal and 
without adhesions to the scar in the skull or brain. The brain 
scar is not visible, its locality being indicated only by the 
arrangement of the surface veins which encircle it. 
In serial sections the lesion is clearly defined for a distance 
of 1.5 mm., of which 1.2 mm. lies posterior to the line of the 
splenium. Throughout its whole extent the wound passes 
through the substantia alba of the occipital lobe, into the cortex 
covering its under surface. Scattered along through the white 
matter there is a considerable amount of unabsorbed blood pig- 
ment which was, however, largely absent from the section of 
which Fig. 2 isa photograph. As will be seen by reference to 
that figure, the cortex on the upper surface of the hemisphere 
has healed so completely that it is hardly possible to make out 
the path of the knife in the upper two-thirds of the grey mat- 
ter, while in its lower third and in the substantia alba the lesion 
is clearly visible. Although the distribution of the fibers in 
the upper region of the cortex is quite normal, the knife must 
have passed through this area to have reached the structures 
below. 
Somewhat lateralward to the wound in the upper part of 
the hemisphere is a peculiar aggregation of fibers in the cortex 
covering the ventral surface. This region is shown in more 
detail in Fig. 9. The dark granular masses indicate the line 
along which the knife has passed. Numerous fibers running 
downward from the white matter are seen to follow this line 
and on approaching the ventral surface to spread out in a fan- 
shaped area. Nerve fibers in considerable numbers may be 
seen crossing the site of the lesion. Especially is this notice- 
able just below the substantia alba (Ff). 
