The surface of the chorion is covered evenly with minute villi, constituting a diffuse non-deciduate placenta.
The small intestine is of great length (80 to 90 ft.), its mucous membrane being covered with numerous fine villi.
In mammals both caecum and colon are often sacculated, a disposition caused by the arrangement of the 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 contrivances for increasing the absorbing surface without adding to the general bulk of the organ, such as the numerous small tags, or " 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 " valvulae conniventes " of man form well-known examples.
If we take a germ free normal animal it has beautiful villi and no inflammation.
Characteristic of coeliac disease is varying degrees of stunting of the small intestinal villi.
