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- 

 vulce connwentes. 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 Lieberhnhn 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 Bruimer 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, disappearing 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 villi 

 and no true valvulie 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 intestinalis), 

 secreted by the mucous glands and follicles. In the jejunum and ileum the 

 chyle is absorbed by their numerous villi; the length and tortuosity of the 

 tube, and its numerous valvule 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 ])onctrate 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 caecum. In their 

 passage along this part of the canal, the absorbents may probably continue 

 902 



