In addition to the ordinary longitudinal and transverse fibres, the colon presents three remarkable muscular bands running along its whole length, and one of which is represented on the colon in the figure on page 155. On the rectum all the three bands are seen. It is in the colon and rectum that the feculent matter accumulates before it is thrown out of the bowels, and these bands are useful chiefly by adding to their propelling power. The natural tendency of muscular fibre being to contract it may naturally be supposed that, after the intestine is emptied, its opposite sides will come into contact, and, by thus obliterating the cavity altogether, present an obstacle to the subsequent passage of any solid matter. But on inspecting the abdomen after death, we rarely meet with any considerable portion thus contracted; and in general, the whole intestines are distended to a greater or less degree, according to circumstances. The agent by which this effect is brought about, is one known more familiarly by the inconveniences and pain to which it gives rise when in excess, than by its proper uses, which are nevertheless important. I allude to the presence of air in the bowels, which is as necessary to their healthy action as their muscular contraction itself. Air, in fact, by its expansive energy, forms the antagonist power to the muscular coat, and serves to dilate the bowel after the requisite contraction has propelled its contents. A certain degree of distention, indeed, not only is a stimulus to farther muscular contraction, but is useful in facilitating the passage of the subsequent portions of the feculent matter; and hence the injection of air into the bowels in large quantity, has lately been employed successfully in overcoming obstinate constipation. The _mucous_, _internal_, or _villous_ coat of the intestine, also resembles in many respects that of the stomach. It is a soft velvety membrane, full of wrinkles or folds through the greater part of its course, by means of which its surface is greatly increased in extent, so as to afford ample space for the ramification of the bloodvessels, nerves, and absorbents, with which it is very plentifully supplied. The cut on p. 172 will convey some idea of its appearance, as seen in the smaller intestine. So far as nutrition is concerned, the mucous coat is the truly _essential_ part of the bowel. It alone is in direct contact with the chyme, and in its cavity the bile and pancreatic juice perform their respective parts, and give rise to the formation of chyle, which is afterwards transmitted from its surface into the general system. The peritoneal and muscular coats are useful only in affording protection, and communicating the power of propelling its contents.