384. Charles R. Stockard. 
Although all parts of the ear are absent the cartilaginous cap- 
sules are present. The shape and size of the capsules, however, 
seem to be adjusted to that of the auditory vesicle when any part 
of it exists, as is indicated on the two sides of fig. 18. 
c. Defects of the central nervous system 
The abnormalities of the brain shown by the specimens treated 
with alcohol might easily form the subject of an extensive mcno- 
graph so various and numerous are they. Only a few of them 
will be briefly mentioned. 
In rare cases the brain is almost normal; the fore brain, however, 
is usually very narrow ard gives to the head a characteristically 
pointed appearance. Dcrsal hernie at times occur in the region 
of the optic lobes and the hind brain. The histological structure 
of the brain is often peculiarly abnormal in both the arrangement 
and the appearance of the cells. The cells may be hyaline and in 
the region of the central cavity fail to take the stains. They may 
even be diffusely scattered in peculiarly defective specimens. 
The spinal cord in some individuals also shows the hyaline 
appearance about its central canal, and spina-bifida in not uncom- 
mon. The latter condition no doubt results from the general 
inhibition in rate of development which is constantly true for 
the specimens in the alcohol solutions. The germ ring is slow in 
surrounding the yolk and consequently the trunk region of the 
early embryo is abbreviated. This condition interferes with the. 
median cell proliferation forming the spinal cord so that a split 
or divided cord results and may extend for various distances in 
the trunk region. Fig. 19 shows a section through a trunk region 
with a double cord, ch, the notocord, nch, is also divided. Fig. 
20 is a more posterior section of the same embryo and shows the 
cord and notocord again single as they are in more anterior region 
than that shown by fig. 19. 
Many of the defects of the central nervous system are of a 
general nature and almost any substance that inhibits or inter- 
feres with the normal developmental rate may cause them. The 
writer does not intend to convey the idea that these are characteris- 
4 jee 
