The alimentary canal of the Sauropsida
is generally divided
into an oesophagus, a simple stomach, a small intestine and
large intestine, which last always terminates in a cloaca. It
is invested by a peritoneal coat, which generally follows all
the curvatures of the intestine. But in the Ophidia
, the folds
of the small intestine are united by fibrous tissue, and enclosed
by a common sheath of peritonaeum.
The stomach is usually a simple dilatation of the alimentary
canal, the cardiac and pyloric apertures of which are
remote from one another; but, in the Crocodiles, and in most
Birds, the pyloric and cardiac apertures are approximated. In
, there is a pyloric dilatation before
the commencement of the duodenum.
In the Crocodilia
, and in Aves, the walls of the stomach
are very muscular, and the muscular fibres of each side radiate
from a central tendon or aponeurosis.
The thickening of the
muscular tunic of the stomach attains its maximum in the
graminivorous birds; and it is accompanied by the develops
ment of the epithelium into a dense and hard coat, adapted
for crushing the food of these animals. Birds commonly aid
the triturating power of this gastric mill by swallowing stones;
but this habit is not confined to them, crocodiles having been
observed to do the same thing.
Birds are further remarkable for the development of a
broad zone of glands in the lower part of the oesophagus,
which is usually dilated, and forms a proventriculus
by a narrow neck with the above-mentioned muscular stomach
or gizzard (gigerium
have a caecum at the junction of the small
intestine with the large; and two such caeca, which sometimes
attain a large size, are very generally developed in Aves
this class also, the small intestine, not unfrequently, presents
a caecal appendage, the remains of the vitelline duct. The
duodenum of Birds constantly makes a loop, within which the
pancreas lies, as in Mammalia
The liver in the Sauropsida
almost always possesses a
gall-bladder, which is usually attached to the under surface
of the right lobe, but in the Ophidia
is removed to some
distance from it.
A peculiar glandular sac, the Bursa Fabricii
, opens into
the anterior and dorsal region of the cloaca in birds.