THE CORTEX OF THE BRAIN IN THE HUMAN EMBRYO 
DURING THE FOURTH MONTH WITH SPECIAL REF- 
ERENCE TO THE SO-CALLED “ PAPILLA OF RETZIUS.” 
BY 
GEORGE L. STREETER, M.D., 
Associate Professor of Neurology at the Wistar Institute. 
WitTH 6 FIGURES. 
The observations reported in the following paper conclusively show 
that the cortical granulations, or papilla of Retzius, caused by the fungi- 
form arrangement of the cells of the pyramidal layer, and commonly 
found in human embryos between 11 and 14 cm. long, constitute an ab- 
normal condition, which is produced either by intrauterine or postpartum 
maceration. It is pointed out that of two human brains of the same age 
one may have cortical papillae while in the other they may be absent. 
Furthermore, it is shown in pig brains, where cortical papille are not 
normally present, that it is possible by experimental methods to produce a 
fungiform clumping of the cortical cells that exactly duplicates the 
condition seen in human brains. 
Attention was first called by Retzius, 95, p. 17, to the fact that human 
brains, usually of the fourth month and more rarely of the fifth month, 
possess a fine granulated character perceptible through the smooth surface 
of the cortex, and in places where the thin superficial layer (Randschicht 
of His) had been torn off they appear correspondingly granulated or cov- 
ered with rounded elevations. Microscopical examination of sections of 
these regions revealed the fact that the granulated character was due to an 
unequal growth of the pyramidal cell layer, which projected in rounded 
elevations, the spaces between which were filled in by the superficial or 
molecular layer, so that the surface of the brain remained smooth. 
Retzius considered the possibility of this granulation formation being 
a manifestation of some pathological process, such as is commonly asso- 
ciated with abortion, e. g., syphilis. He was, however, more inclined to 
believe it a normal condition due to a transitory exuberant growth of the 
pyramidal cell layer, the surface irregularities caused thereby being 
AMERICAN JOURNAL OF ANATOMY.—VOL. VII. 
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