. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. Intestinal tubes from the jejunum, as seen in a vertica section. (Magnified 80 diameters.} a, Limitary or basement membrane; b, nuclei of the columnar cells which line its interior ; c, calibre or cavity of the tube ; d, mouths of the tubes opening into the general cavity of the intestine ; e, blind extremities of the tubes, corresponding to the sub- mucous areolar tissue. blind extremity. Its average diameter is about irtjo1'1 °f an inch, except at its orifice, where it is somewhat wider. The lower part of the tube is o
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. Intestinal tubes from the jejunum, as seen in a vertica section. (Magnified 80 diameters.} a, Limitary or basement membrane; b, nuclei of the columnar cells which line its interior ; c, calibre or cavity of the tube ; d, mouths of the tubes opening into the general cavity of the intestine ; e, blind extremities of the tubes, corresponding to the sub- mucous areolar tissue. blind extremity. Its average diameter is about irtjo1'1 °f an inch, except at its orifice, where it is somewhat wider. The lower part of the tube is often slightly enlarged: and rarely it appears to bifurcate. But while it is doubtful whether these appearances can be depended upon*, it is certain that they are not sufficiently marked or frequent to alter the above general This cylindrical tube is composed of base- ment membrane and epithelium. The former constituent needs no special description. The latter is a single layer of short columnar cells. It clothes the whole interior surface of the tubes ; and becomes continuous, at their upper extremities, with the epithelium covering the villi, the constituent cells of which generally appear to be somewhat longer in shape. The cylindrical cavity bounded by these cells has * See foot-note to p. 321. t A more valid exception to the above statement may be found in the upper part of the duodenum of some of the domestic Mammalia; in whom many of these tubes divide, a little below the surface, into three or four smaller ones. This condition may be regarded as a transition from the structure of either the pyloric tubes, or the clustered glands of Brunn, to that of the ordinary intestinal tube. From the appearances offered by the cylindrical epithelium that lines their interior, the first of these conjec- tures may be regarded as the more probable of the two. a diameter which amounts to about one-fourth the width of the entire tube. The arrangement of these tubes so pr
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