1012 THE DIGESTIVE SYSTEM. 
the intestinal tube, must next be considered: these are the (1) vill; (2) valvulee 
conniventes ; (3) solitary glands; and (4) agminated glands, or Peyer’s patches. 
Villi (villi intestinales)—If the mucous membrane of any part of the small 
intestine be examined, it 1s seen to present a soft, velvety, or fleecy appearance 
(Fig. 685, B); this is due to the presence of an enormous number of minute pro- 
cesses, leona ‘i as villi, which cover its surface. 
Villi are minute cylindrical or finger-hke projections of the mucous membrane 
(Fig. 684), about 344th or zoth of an inch (1:2 to 1-6 mm.) in height, and barely 
visible to the naked eye, which are closely set all over the surface of the mucous 
membrane of the sinall intestine. Beginning at the edve of the pyloric valve, they 
are said to be broader but shorter in the duodenum, and to grow narrower as they 
are followed down through the intestine to the ileo-czecal v alve e, at the edge of which 
they cease. They are found, not only on the general surface of the mucous 
membrane, but also upon the valvule conniventes, ‘and, while they are not present 
over the solitary glands, they are found in the intervals between the individual 
nodules of the Peyer's patches. 
They are connected with the absorption of the products of digestion which 
takes place in the small intestine. 
Valvule Conniventes (plicee circulares).— When the intestine is empty and 
contracted, 1ts mucous membrane may in places be thrown into effaceable folds or 
ruge, which disappear on distention. But in addition to these, there are found 
in certain portions of the small intestine a series of large, permanent folds, which 
are not effaceable ; these are known as valvulee conniventes (Fig. 685). They are 
usually more or less crescentic in shape, and resemble a series of closely-placed 
shelves running transversely around the gut. They rarely form more than two- 
j thirds of a circle; 
sometimes, how- 
ever, they present 
a circular or even 
a spiral arrange- 
ment, the spiral 
extending — little 
more than once — 
round the tube, — 
as a rule. Occa- 
sionally they hi- 
furcate at one 
or both ends; 
sometimes, too, 
short irregularly 
‘lirected branches 
pass off from 
them. They are 
usually about 2 
to 5 inches (5 to 
Fic. 685.—VaLVUL& CONNIVENTES (uatural size). 7 cm.) 1m length, 
A, as seen in a bit of jejunum which has been filled with alcohol and hardened ; and their breadth, 
B, a portion of fresh intestine spread out under water. that is their pro- 
jection into the 
cavity, may be as much as 4rd of an inch (8 mn. ), whilst in thickness, as seen 
when cut across, they measure about {th inch (3 mm.) 
They are composed of two layers of mucous membrane, placed back to back, 
with a little submucosa between, to bind the two together, and are covered with 
villi and Lieberkiihn’s glands. Their use is to increase the amount of surface 
available for secretion and ab sorption. 
Valvulee conniventes are not found in the upper part of the duodenum for 
distance varying from 1 to 2 inches (2°5 to 5 em.) from the pylorus. Here they 
begin, and are at first small, irregular, and scattered; but they grow graduall 
larger as we pass down, and when the opening of the bile-duct is reache 
Sn "we ae SS GE 
