42 



STUDIES ON THE LONGITUDINAL MUSCLE OF THE HUMAN COLON. 



The development thus far attained is fundamental, remaining unchanged in its 

 essential features throughout subsequent variations in size, shape, and relationship 

 of the colon. Changes may be noted in its form, as when contractions of the cir- 

 cular muscle produce saccules, or in its position and relationship, as when markedly 

 filled by meconium; but the bands never lose their identity, nor do the intervals 

 become entirely obliterated. In a region of the bowel where there is marked dis- 

 tension and the wall is smoothed out the taeniae remain distinct, and over the domes 

 of the saccules there may be found a very thin layer of longitudinal fibers. It is 

 generally stated that the taeniae become confluent in the lower end of the bowel, but 

 cross-sections show that the three bands are still present as thickenings in the wall, 

 distinctly separated from each other, although sacculations are absent. 



The second phase of taeniae formation is ushered in by a factor which begins 

 about the 150-mm. stage — i.e., the appearance of sacculations, the effect of which 

 upon the taeniae is significant. Their formation and effect were studied experi- 

 mentally in the guinea-pig; investigations were also made of skiagrams of the 

 human colon and a few direct inspections in fife, through the 

 fluoroscope. By these methods it was directly observed that the 

 pouches are produced by the sharp contraction of narrow groups 

 of circular muscle-fibers extending between adjacent taeniae. 

 Apparently the circular muscle is more or less firmly attached 

 by inter-muscular connective tissue to the longitudinal bands, 

 which fact permits it to contract segmentally. The fluoroscopic 

 inspections and the experiments on the caecum of the guinea-pig- 

 showed waves of contraction passing down the bowel in three 

 rows, between the three taeniae, which constantly changed its 

 surface contour from a series of saccules to a series of clefts. 

 The degree of contraction varied from a slight indentation of 

 the saccule to its entire obliteration. 



A marked feature noted was that the contraction waves 

 were independent of each other; only rarely were two groups of 

 fibers on opposite sides of taeniae in contraction at the same time. 

 Most commonly a contracting segment was opposed by a saccule; 

 thus the three rows of saccules are also independent of each other 

 (fig. 8) . The saccules are in no way related to the bowel-con- 

 tent, as evidenced by the fact that they appear as early as the 

 150-mm. stage in a region of the colon where there is no meco- 

 nium, and that where meconium is causing the distension the 

 saccules are absent. For the production of both taenia' and 

 saccules it is evidently necessary to seek further than meconium 

 distension or stimulation caused by it. A basis for such a study might be found 

 in the peculiar position of the pig's taeniae and their relationship to the mesen- 

 teric structures, nerves, blood-vessels, and lymphatics. 



Recalling the position of the two taeniae, one on each side of the bowel with none 

 at the mesenteric attachment, it is interesting to note that, instead of the mesenteric 

 structures entering the intestinal wall at the mesenteric line, the majority of them 



-Semi-diagram- 

 matic figure of colon 

 of a new-born infant, 

 showing alternate 

 arrangement of sac- 

 cules on opposite 

 sides of a tsenia. 



