74 MARION HINES 
this paper to establish landmarks in the growth and differentia- 
tion of the telencephalon, such that accurate measurements 
of the varied components of the developing cerebral hemispheres 
may be taken. Such a purpose is the outcome of a considera- 
tion of the question, long a mooted one, of early telencephalic 
fissuration. That history is complicated by a group of uncor- 
related and seemingly contradictory facts, which bear the names 
of the most eminent neurologists and embryologists of the latter 
part of the nineteenth century. The solution of that problem 
depends upon a more modern technique and a consideration of 
histological structure. 
The reality of certain fissures which appeared in the medial 
wall of the cerebral hemispheres of the human embryo between 
the second and the fourth months was under debate from 1868 
to 1904. These fissures were variously named, the most impor- 
tant being the arched fissure (or the Bogenfurche, the fissura 
ammonis, the fissura hippocampi) and the fissura prima. The 
Bogenfurche was divided into an anterior and a posterior limb and 
sometimes radial folds and an arched accessory fissure were 
added. Are they real or are they artefacts? If they are real, 
why do they disappear after four and a half months and seem to 
play no part in the future fissuration of the medial wall? Pre- 
vious investigators answered them each in his own manner. 
Those answers have a peculiar bearing upon the present 
discussion. 
HISTORY 
Meckel (1815) thought that fissures appeared on the medial 
wall which later ‘‘grew into each other, so that the surface of the 
brain both inside and outside again becomes smooth.” ‘Tiede- 
mann (1816) pictured them, but did not consider them to be 
transitory; rather, he thought them to represent earlier condi- 
tions of permanent sulci. The study of the central nervous 
system remained fifty years where Tiedemann had left it. Bis- 
choff (’68) reported these fissurations as due entirely to alcoholic 
fixation. However, in the next year, Ecker reported finding 
them in the fresh brains of mammalian embryos. Schmidt 
(92) referred to these fissures as temporary furrows, but failed 
