region
of the anterior appendage, at the point marked _X_, it divides into the
two very short bronchi, which almost immediately open into the lungs,
_lu_. The lungs, whose structure will be shown in the sections of this
stage, are large, irregular bodies, extending about equal distances
cephalad and caudad to their openings into the bronchi. The caudal ends
of the lungs overlap the cephalic end of the liver, _li_.

The oesophagus, _oe_, is large, and is laterally compressed so that its
dorso-ventral diameter, the one shown in the present figure, is two or
three times as great as its lateral diameter. This gives the impression,
in the reconstruction, that the oesophagus is nearly as large as the
stomach.

As has been said, the oesophagus does not open directly into the
pharynx, but is separated from it by a membrane which consists of the
flattened epithelial layers of both cavities separated by a thin layer
of mesoblast. This partition between the pharynx and the oesophagus is
not a mere fold of mucous membrane, but is a complete, though thin,
wall, easily seen in the series of sagittal sections from which this
region of the embryo was drawn. The anterior end of the oesophagus is
suddenly constricted so that the actual opening closed by this partition
is not large.

Followed caudad the dorso-ventral diameter of the oesophagus varies
somewhat, as does the lateral diameter, but it remains large throughout
and opens into the stomach with no sharp line of demarkation. The
character of the epithelium of the enteron caudad to the pharynx will be
discussed in connection with the sections to be described below.

The stomach, _i'_, is very different in outline from what was seen in
the last stage described, figure 6A. Instead of having approximately the
form of the typical mammalian stomach it is now so elongated that the
opening into the duodenum, the pylorus, _py_, seems to be nearer the
anterior than the posterior end. While the position of the pylorus is
very distinct it is difficult to distinguish the line of demarkation
between the stomach and the oesophagus.

The extreme caudal region of the stomach is enlarged to form a blind
sac, representing the gizzard, _gz_. A slight enlargement in the region
of the pylorus may represent the glandular region of the adult stomach.
The stomach opens, in a rather curious way, into the side of the
duodenum, _d_, the anterior end of the latter structure having the
appearance of a so