804 Proceedings of Royal Society of Edinburgh. [sess. 
(Plate I. fig. 2). These are lined by cubical epithelial cells, and 
the secreting tubules branch and run irregularly in the deeper 
part of the membrane. The connective tissue, which is some- 
what altered near the surface, probably by digestion, is dense, 
and in an intermediate zone consists very largely of cellular con- 
nective or lymphoid tissue. In the deeper parts the lymphoid 
character is not so well marked, although nuclei are still numerous. 
The terminations of the glands rest on a connective tissue mucosa, 
in which numerous blood-vessels are found. 
The Fourth True Digestive Cavity. 
This, the last of the cavities into which the stomach is sub- 
divided, is cylindrical in form, and measures 9J inches in length 
by 2f inches in diameter. The orifice by which it communi- 
cates with the intestine, viz., the pyloric, is capable of being 
distended to a diameter of three-fourths of an inch, and 
is situated about an inch from the distal end of the cavity, a 
short csecal pouch being thus formed. The mucous membrane is 
similar in appearance to that of the previous compartments, but is 
smooth, and almost devoid of rugae. The pylorus is represented 
by a well-marked elevation of the mucous membrane, wdiich, how- 
ever, is blunt, and rounded at its free edge. 
Structure of the Walls . — The outer coats are much the same as 
in the previous compartments, but the longitudinal layer of fibres 
of the muscular coat is very poorly developed, and, with the excep- 
tion of a few fibres, is, in most parts, absent. Nerve ganglion 
cells are present as in the wall of the two previous compartments. 
The arteries in the submucous coat are numerous, and are remark- 
able for the thickness of their muscular, and the denseness of their 
adventitious, coats. 
Mucous Membrane . — The glands are very similar in their struc- 
ture to those of the previous compartment (Plate I. fig. 2 ) ; the 
lower parts of the glands frequently branch, and form transverse or 
acute bendings. Small patches of lymphoid tissue are present, and 
there are delicate bundles of muscular fibre lying parallel to the 
axes of the glands. 
The third and fourth true digestive cavities, though separated by 
a somewhat narrow opening, are very similar to one another in all 
