ALIMENTARY SYSTEM — STOMACH. 
277 
Tlie Stomach or miil-iutestinal sac is a specialized enlargement of 
the digestive tube, in or near to which the chief digestive processes 
are performed and whose walls are often thickened and strengthened 
by constrictor muscles, and although, in 
many species, the stomach seems blended 
morphologically and functionally with the 
crop, the two organs are often perceptibly 
distinct. It is usually of an elongate or 
ovoid form, but, being placed at and forming 
the termination of the first alimentary tract, 
it is often so bent and curved as to seem a lateral outgTOwth of the 
alimentary tube, the cardiac or oesophageal and the pyloric or intestinal 
apertures becoming more closely approximated in proportion to the 
abruptness of the angle formed by the returning tract. 
Fig. 550. — Epithelial cells 
from stomach of Helix pom atia 
L., highly magnified (after V ogt 
and Yung). 
Fig. 551. — Interior of stomach of 
CyclosioDia ele^^ans (Mull.), x 4, showing 
its complicated and sacculate walls (after 
Garnault). 
ce. oesophagus ; i. intestine ; d.g. diges- 
tive glands and ducts. 
Fig. 552. — Section through the walls of the 
stomach of Helix pomatia L., highly magnified 
(after Vogt and Yung). 
cti, cuticle ; e.c. cylindrical nucleated epithelial 
cells with interposed lacunas ; 7ti. muscular layer 
with nucleated connective tissue. 
Interiorly the walls of the stomach are beset with glands secreting a 
digestive fluid and thrown into longitudinal folds continuous with 
those of the oesophagus and often 
crossed by more indistinctly trans- 
verse ones, giving the stomach a 
somewhat sacculate aspect. There 
is often a coecum or accessory sac 
on the right side in the pyloric 
region, the Stylotheca (cttuXos, a 
rod ; 9i]K7], a receptacle), which may 
extend between the convolutions of the intestines, and contains the 
Fig. 553. — Alimentary tract of Dreissensia 
polymorpha (Pall.), more especially to illus- 
trate the position and character of the Stylo- 
theca (after Moquin-Tandon). 
in. mouth ; st. stomach : p. plecton ; r. 
rectum piercing the heart, h. ; s.c. pyloric 
coecum or stylotheca. 
