Opis

The longitudinal layer (longitudinal fibers) do not form a continuous layer over the whole surface of the large intestine.

In the cecum and colon they are especially collected into three flat longitudinal bands (tænæi coli), each of about 12 mm. in width;

  • One, the mesocolic taenia, is placed posteromedialy along the attached border of the intestine;
  • The omental taeni, the anterior and the largest, corresponds along the arch of the colon to the attachment of the greater omentum, but is in front in the ascending, descending, and iliac parts of the colon, and in the sigmoid colon;
  • The third, the free taenia or lateral band, is found on the medial side of the ascending and descending parts of the colon, and on the under aspect of the transverse colon.

These bands are shorter than the other coats of the intestine, and serve to produce the sacculi which are characteristic of the cecum and colon; accordingly, when they are dissected off, the tube can be lengthened, and its sacculated character disappears.

In the sigmoid colon the longitudinal fibers become more scattered; and around the rectum they spread out and form a layer, which completely encircles this portion of the gut, but is thicker on the anterior and posterior surfaces, where it forms two bands, than on the lateral surfaces.

In addition, two bands of plain muscular tissue arise from the second and third coccygeal vertebræ, and pass downward and forward to blend with the longitudinal muscular fibers on the posterior wall of the anal canal. These are known as the Rectococcygeal muscles.


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