342 The “ Papille of Retzius” and the Cortex of Embryos 
B. Maceration Followed by Good Fixation. 
B1. Maceration in normal salt solution (11.5 cm. pigs) 
(a) Fresh brain placed in salt solution, 28 hours. 
Hardened in chrome-acetic solution, 48 hours. 
Washed, dehydrated and sectioned in celloidin. 
(b) (Figs. 4 and 6) Fresh brain placed in salt solution, 48 hours. 
Hardened in formalin 10%, 24 hours. 
Secondary fixation in Miiller’s solution, 4 days. 
Washed, dehydrated and sectioned in celloidin. 
B2. Maceration in its own fluids (11.5 em. pig) see Fig. 5. 
Embryo left exposed to air, 48 hours. 
Brain removed and kept in formalin, 48 hours. 
Secondary fixation in Miiller’s solution, 4 days. 
Washed, dehydrated and sectioned in celloidin. 
The sections of the specimens macerated in salt solution (B1, a and b) 
show fairly good preservation of the deeper lying parts, there is almost 
no shredding of the tissue like that seen in the specimens in which the 
penetration of the fixing fluids was hindered by the brain coverings. The 
pyramidal layer of the cortex, however, is found to be thrown into irregu- 
lar folds, accompanied by a fungiform clumping of its constituent cells. 
This appearance is present in both specimens, but is more marked in the 
specimen (0) macerated 48 hours. A section of this was photographed 
and is reproduced in Fig. 6. The resemblance is close to the description 
given by His and Retzius of the cortical papilla in the human embryo. It 
has the same smooth-surfaced superficial layer, which dips down between 
the papillae of the subjacent pyramidal layer. In some places these in- 
cisures cut off small irregular islands of pyramidal cells. The inner 
surface of the pyramidal layer does not have these sharp notches, but runs 
across the section in an irregular wavy ill-defined line. In addition to the 
fungiform clumping of the cortical cells, in some of the sections the so- 
called transitory fissures are found. These dip sharply inward and invade 
in some cases more than one-third of the thickness of the brain wall. In 
the formation of these, the superficial layer is partially folded in with a 
corresponding cleft on the surface of the brain, which is not the case with 
the cortical papille. It may be noted that the artificial character of 
transitory fissures has been well established by Hochstetter, 98, and Mall, 
03, the latter having examined over fifty embryos and found that accord- 
ing to the effect of various dissociating influences he could obtain macera- 
