196 . ANTHROPOLOGY. ; 
of the stomach, yet presents some peculiarities, the most important of | 
which is seen in the series of permanent folds or duplicatures named val-: 
vule conniventes. These commence in the vertical portion of the duo-. 
denum, and increasing exist in great quantities as far as the upper half of 
the ileum; they then decrease in numbers and size, and are wholly absent, 
in the last few feet of the ileum. They are semilunar folds or arches 
extending round one half or more of the tube, into which they project. 
when this is distended, like shelves. They increase the extent of surface 
of intestine, and delay the food in its downward passage, affording to the 
‘absorbents a better opportunity to take up the chyle. The whole mucous 
surface of the small intestines is furnished with follicles and mucous glands; 
it also presents numerous projecting processes called villi. The follicles 
of Ineberkuhn are simple pouches of the membrane, very small, and scat-. 
tered numerously over the whole surface. The more elaborate glands 
present different appearances. The glands of Brunner are chiefly in the. 
duodenum, in the submucous tissue, and surround the intestine in a lamina 
of white bodies. The glands of Peyer are found chiefly along the convex, 
part of the intestine, sometimes single, sometimes aggregated. The func-. 
tion of these glands is unknown. The villi are those short cylindrical or, 
conical processes seen so abundantly on the mucous membrane of the small 
intestine ; when examined under a lens they are found to be covered. by a 
fine membrane in addition to the epithelium, and to contain a minute plexus 
of blood-vessels through the medium of which the absorption of fluids for 
the canal takes place. The lacteal vessels commence in each villus. by 
small branches, but they do not open on the surface by free orifices as was 
at one time supposed. At the extremity of each villus are seen small 
vesicles during the presence of food in the intestines, disappearmg when 
this is empty. These in all probability are developed from nuclei by 
absorption of matter from the descending food, and soon burst, discharging 
their contents inwards towards the lacteals. Free fluids are probably taken 
up directly by endosmosis through the veins distributed along the intestinal 
tract. 
The mucous membrane of the large intestine differs in having no vill 
and no true valvulz conniventes. Internally are seen several crests or semi- 
lunar folds; these, however, are formed by all the coats, and not by the 
mucous membrane alone as in the small intestine. 
As the food is propelled onwards through the intestines, both large and 
small, it becomes mingled with a vast quantity of fluid (succus itestinalis), 
secreted by the mucous glands and follicles. Inthe jejunum and ileum the 
chyle is absorbed by their numerous villi; the length and tortuosity of the 
tube, and its numerous valvulze conniventes, are admirably adapted to 
increase the extent of this secreting and absorbing surface, and at the same 
time to retard the progress of the food, and to penetrate and subdivide the 
mass, so as to search out, as it were, and extract all the nutriment or chyle 
it may contain. In the large intestine the contents acquire their feculent 
properties, the first traces of which they exhibit in the ccecum.- In their 
passage along this part of the canal, the absorbents may probably continue 
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