262 The Alligator and Its Allies 
the entoderm being almost flat and horizontal. 
The notochord (nt) is distinctly outlined and is 
somewhat flattened in a dorso-ventral direction. 
The body cavity (bc) is well marked, but is sepa- 
rated by a considerable mass of uncleft mesoblast 
from the notochord and the walls of the medullary 
groove. 
A space of about one hundred sections, or one 
third the length of the embryo, intervenes between 
Figures 9gandgz. This is the region of the meso- 
blastic somites, and in this region, as has been 
above stated, the medullary canal is completely 
enclosed. It is evident then that the entire ante- 
rior two thirds of the medullary canal is enclosed 
except for the short region represented in Figure 8g. 
Whether or not this short open region between the 
two longer enclosed regions is a normal condition 
the material at hand does not show. 
Figure 9/ represents a typical section in the 
region of the mesoblastic somites just described. 
It shows the enclosed medullary canal (mc), the 
body cavity (bc) on the right, and a mesoblastic 
somite with its small cavity (myc) on the left. 
The entire section is smaller than the sections 
anterior or posterior to this region, and seems to 
be compressed in a dorso-ventral direction, this 
compression being especially marked in the case 
of the notochord. 
Figure 97 is through a region nearly one hundred 
sections posterior to the preceding, and cuts the 
