88 Walter E. Dandy. 
of the umbilical vesicle is drained by the sinus ensiforme. The ento- 
dermal lining of the inner surface of the umbilical vesicle forms a dis- 
tinet layer in places, whereas in other locations, especially in the 
ventral half, no definite layer of cells can be made out, so intimately 
is it fused with the knotty and thickened mesoderm. 
Amnion.—The amnion is a completely closed cavity, with very thin 
delicate walls of flattened cells, the imdividuality of ectoderm and 
mesoderm being everywhere beautifully preserved. The cavity of the 
amnion is very large, probably due, as suggested by Professor Mall, 
to the osmosis of large quantities of dilute formalin in which it was 
preserved for over two years. Anteriorly a rather deep pocket of 
amnion dips ventral to the heart, evidently a sign of posterior exten- 
sion of the head fold. The tail fold is very small, covering the 
embryo for a distance of only 5 or 6 sections. 
GENERAL APPEARANCE OF THE EMBRYO. 
The embryo presents an anterior and posterior elevation with a 
marked dorsal link. (Plate IV.) The anterior elevation is gradual, 
the posterior very sharp, rising at an angle of about 80°. This kink 
seems to be partly natural and partly an exaggerated post-mortem 
condition. We should naturally expect a dorsal concavity due to 
the greater development of the structures in both the anterior and 
posterior regions of the embryo. ‘The marked accentuation how- 
ever may be due, as suggested by Professor Mall, to the large 
amnion filled with fluid, the weight of which would naturally act 
upon the point of least resistance. Shrinkage incident to manipula- 
tion and imbedding also plays an important role in its aggravation, 
especially after location of the point of least resistance. This is 
clearly shown by a comparison of the model with a sketch of the 
embryo before imbedding, there being an accentuation of the kink 
by almost 15°. 
EcropERM. 
Nervous system. The extent of development of the nervous sys- 
tem is a medullary groove, open throughout its entire length. The 
brain region is divided into three primary vesicles (Plate VI), the 
anterior being equal in size to the other two combined. The first or 
