THE DIGESTIVE SYSTEM 59 
Brunner’s glands, the pancreas, and the liver; the position of the 
ducts of the two latter organs being indicated in Fig. 20. 
Intestinal Canal.—The intestinal canal varies greatly in relative 
length and capacity in different animals, and it also offers manifold 
peculiarities of form, being sometimes a simple cylindrical tube of 
nearly uniform calibre throughout, but more often subject to altera- 
tions of form and capacity in different portions of its course,—the 
most characteristic and constant being the division into an upper 
and narrower, and lower and wider portion, called respectively the 
small and the large intestine, the former being divided quite arbi- 
trarily and artificially into duodenum, jejun- 
um, and ileum, and the latter into colon and 
rectum. One of the most striking peculiari- 
ties of this part of the alimentary canal is 
the frequent presence of a diverticulum or 
blind pouch, the caput cecwm coli, as it was 
first called, a name generally abbreviated into 
“cecum,” situated at the junction of the 
large and the small intestine, a structure pre- 
senting an immense variety of development, 
from the smallest bulging of a portion of the 
side wall of the tube to a huge and complex 
sac, greatly exceeding in capacity the whole 
of the remainder of the alimentary canal. It 
is only in herbivorous animals that the caecum 
is developed to this great extent, and among 
these there is a curious complementary re- ; ' 
< a . : Fia, 21. — Diagrammatic 
lationship between the size and complexity pian of the general arrange- 
of this organ and that of the stomach. ment of the alimentary canal 
Where the latter is simple the cacum is i ® typical Mammal 
a sophagus; st, stomach; p, 
generally the largest, and vice versd. Both the pylorus; s,s, small intestine 
cecum and colon are often sacculated, a dis- (abbreviated); ¢, cwcum ; J, J, 
position caused by the arrangement of the ae oe 
longitudinal bands of muscular tissue in their ~ 
walls; but the small intestine is always smooth and simple-walled 
externally, though its lining membrane often exhibits various 
contrivances for increasing the absorbing surface without adding to 
the general bulk of the organ, such as the numerous small villi by 
which it’ is everywhere beset, and the more obvious transverse, 
longitudinal, or reticulating folds projecting into the interior, met 
with in many animals, of which the “ valvul conniventes” of Man 
form well-known examples. 
Besides the crypts of Lieberkuhn found throughout the in- 
testinal canal, and the glands of Brunner confined to the duodenun, 
there are other structures in the mucous membrane, about the 
nature of which there is still much uncertainty, called “solitary ” and 
