336 Transitory Fissures of the Human Cerebrum 
cord is not macerated very much, but when the entire central nervous 
system is macerated and solid it is marked 5. So we have, in addition 
to the embryos in which the surfaces of the brain are smooth, those in 
which the cerebral vesicles are folded and macerated from the simple 
small fold up to a stage in which the entire central nervous system is 
converted into a pulpy mass. 
It is seen from the table that the condition of the brain varies very 
much in embryos of the first month as well as in the later months. In 
four of the embryos the cerebral vesicles are perfect and these are from 
specimens which were carefully hardened. In the fifth, No. 80, there 
are no data except that the specimen was hardened in alcohol. One 
embryo, No. 164, is from an autopsy, and the uterus after it had been 
cut open was kept on ice for 24 hours before it came into my hands. 
The entire specimen was then placed in strong formalin. Since all of 
the sections show that the tissues of the body are macerated it is not 
difficult to understand why the walls of the cerebral vesicles are also 
macerated and slightly folded. 
The embryos of the second month also show a variety of conditions in 
the cerebral vesicles. There are six perfect ones and three of these were 
hardened in formalin. One formalin specimen, No. 106, is pretty well 
macerated, but the specimen had been in water 24 hours before it came 
into my hands. In it the brain and spinal cord are practically sold. 
In No. 86 there is one small fissure on the medial and one on the lateral 
side of the cerebral hemisphere. This embryo was brought to the labo- 
ratory with the amnion unbroken, and without opening it the entire 
specimen was placed in formalin. It may be that the shght amount 
of formalin which entered the embryo first acted as a dissociator, caused 
the cerebral vesicles to expand quicker than the membranes and these nar- 
row transitory fissures followed. In this specimen the fissures are 
formed by the epithelial wall of the cerebral vesicle turning in without 
drawing the pia with it. he pia bridges straight over the transitory 
fissure and the capillaries to the cerebral vesicle are torn off. It is 
clearly a case of tearing the cerebral vesicle from the pia, which could 
only have taken place after the death of the embryo. 
During the third month it is said that the transitory fissures make 
their appearance. Among ten specimens there are two with perfect 
transitory fissures and three with well marked transitory fissures. There 
are five specimens without any fissures at all and four of them are for- 
malin specimens. One specimen, No. 95, has well-marked total fissures 
all around the cerebral vesicle. ‘This specimen came to the laboratory 
fresh and without opening the ovum it was placed in formalin. This 
