356 MALL. [VoL. XIV. 
from the figure that the allantoic stalk and the umbilical vesicle 
must shift their position through a distance of at least twelve 
segments in order to gain the position they will hold in older 
embryos. The possibility of this shifting is all easily under- 
stood when we consider how soft the tissues are at this time, 
and the lack of any framework to hold the different parts of 
the embryo together. Later on, when nerve bundles and 
skeleton appear, the shifting still takes place, but by no means 
to as great an extent, and its course is now marked by the 
arrangement of the nerves as well as other tissues. At this 
stage, however, the most fixed points appear to be the myotomes, 
and from them I have made all of my measurements. For 
reasons given in the earlier descriptions of this embryo I have 
ascribed three of the muscle plates to the occipital region, 
making the first dorsal myotome immediately over the neuren- 
teric canal. In later stages each myotome lies immediately over 
a spinal ganglion, and in referring to the myotomes I give them 
the numbers corresponding to the spinal nerves. This causes 
less confusion than by numbering them from the auditory 
vesicle backward, for by so doing we do not convey any idea 
of adult anatomy. 
In embryos slightly older than the one figured above, the 
spinal ganglia and vertebral column are outlined, thus aiding 
us easily to locate the position of any of the organs. With the 
descent of the heart the communication of the umbilical vesicle 
with the midgut is rapidly cut off, and the stems connecting 
them, together with the allantoic stalk are then encircled with 
the amnion. All these intermediate stages are sufficiently well 
shown in His’s A¢/as, and I need not describe them. 
At the end of the fourth week the umbilical cord is fully 
formed, as is shown by a number of specimens in my possession, 
two of which are especially valuable because there is no doubt 
whatever as to their being normal. One is the specimen I have 
studied a great deal, which was obtained from a criminal abor- 
tion, and the other was gotten from a murdered woman and 
sent me by the coroner’s physician of Chicago. The first 
specimen (No. II) is somewhat older than the second (No. 
LXXVI), and for that reason is more valuable. 
