Franklin P. Mall aot 
was the first of the formalin specimens which was cut, and for a long 
time I considered it conclusive proof in favor of the transitory fissures 
being normal. Here also the slow penetration of the formalin may 
have acted more markedly as a dissociator which caused the cerebral | 
vesicles to expand quicker than the membranous walls of the head and 
thereby produced the slight infolding. In this specimen, as in No. 86, 
the maceration has caused a separation of the cerebral walls from the 
pia over the transitory fissures. At other points the cerebral cells turn 
outward, forming small microscopic protuberances. In both these speci- 
mens the microscopic examination shows clearly that the transitory 
fissures are produced artificially by the unequal expansion of the cerebral 
vesicles and the membranous wall. The walls of the cerebral vesicles 
naturally were torn away from the pia along the line of the transitory 
fissures. 
I was fortunate enough to obtain a fresh embryo of the fourth month 
while tabulating the specimens of my collection. Although the abor- 
tion had taken place 24 hours previously, the brain showed no indica- 
tions of fissures at all; in every respect the specimen was like that of 
Retzius. After the membranous wall had been removed the brain was 
placed in formalin, in which it retained its smooth form. 
The specimens of the fourth and fifth months are very conclusive. 
There are nine specimens hardened in formalin and none of them 
have any transitory fissures. ‘They are present in the four specimens 
which were hardened in alcohol. A single fresh specimen at the begin- 
ning of the fifth month was perfectly smooth on both mesial and lateral 
surfaces, although the embryo came into my possession 24 hours after 
the abortion. 
It is apparent from the specimens which have been described that 
fluids which dissociate tissues are more marked in their effect upon the 
walls of the cerebral vesicles than upon any of the other tissues of the 
embryo. As the cells of the cerebral vesicles become thicker and the 
tissues firmer the brain substance is more resistant and does not macerate 
as easily as before, so that by the fifth month transitory fissures can be 
no longer produced artificially. Formalin, which in strong solutions 
causes the brain tissue to swell, is a dissociator in very weak solutions, 
and therefore occasionally produces transitory fissures. According to 
the experience of Hochstetter, Retzius and myself, the transitory fissures 
are not found in fresh brains. The transitory fissures are therefore arti- 
ficial and are of no morphological significance. 
