STUDIES ON THE LONGITUDINAL MUSCLE OF THE HUMAN COLON. 



41 



and thick, but are not effaced by subsequent growth in the general intestinal wall. 

 They are actually permanent accumulations of muscle-fibers and not temporary 

 migrations of fibers from the adjacent interspaces, since these spaces are entirely 

 unaffected by them. This is somewhat at variance with Broman, who speaks of a 

 splitting of the muscle by dilatation of the intestine which produces the three 

 parallel bands. One may only conjecture what he considers produces the dilatation. 

 That it is a filling of the intestine with meconium is a reasonable deduction, but the 

 formation of the taeniae could hardly be explained on this basis. Meconium accumu- 

 lates first in the rectum. In a 125-mm. fetus it fills the tube to distension only as 

 far as the beginning of the sigmoid, but the taeniae are distinctly formed as early as 



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Fig. G. — Cross-section of the ascending colon of a human fetus 105 mm. CR. length, showing the three tseniaj in a triangular 

 position in the wall. Note their broad, flat shape and the presence of longitudinal fibers in the intervals. 



Fig. 7. — Cross-section of a 200-mm. pig fetus, showing lateral position of the two teniae. Note blood-vessels passing 

 just beneath the peritoneal layer to the vicinity of the bands. 



the 105-mm. stage and in a region where no trace of meconium is found. Further- 

 more, in this rectal region, where there is marked distension with distinct taeniae, 

 the interspaces are unbroken. In the new-born, distension with meconium may be 

 found as high up as the caecal region, but the ring of longitudinal fibers remains 

 unbroken ; hence a splitting process can hardly be considered. From his statement 

 that "there is probably a thin layer of longitudinal muscle in the interval between 

 the taeniae," it may be concluded that Lewis holds that the taeniae are present first, 

 and that later the interspaces are filled in by extension from the edges of adjacent 

 bands; but from a careful study of young series up to the 100-mm. stage I am led 

 to believe that the muscle is first present as a continuous layer, probably having 

 grown laterally from the horns of the mesenteric crescent — the first band — and that 

 the other two taeniae develop within the layer as aggregations of muscle-fibers. 



