40 



STUDIES ON THE LONGITUDINAL MUSCLE OF THE HUMAN COLON. 



sponding to the mesenteric tseniae in man. The other two taeniae continue their 

 lateral position also to the tip of the caecum. 



The problem of the taeniae has been thus far suggested only by way of citing 

 the mesenteric thickening and its relationship to the rest of the muscle. Lewis 

 referred to this as the mesenteric lamia and stated that "at 99 mm. it is still the most 

 prominent part of the longitudinal muscle"; and further, that "the other two 

 taeniae are indicated." Broman stated that in the fourth month the primordia of 

 the longitudinal muscle bundles are marked. One feels that both of these state- 

 ments are incomplete, since one does not make it clear where or by what the taenia) 



1 1 





Fig 4 —Cross-section of the colon of a human fetus 52 mm. CR. length, showing a well-defined tenia at the mesenteric arc. 



with a complete layer of loosely scattered fibers surrounding the tube. _.,..,., . . , . 



Fig 5 -Cross-section of a human fetus 90 mm. CR. length, showing the fibers of the longitudinal muscle, loosely scattered 



in the 52-mm. stage, now compact, and only the mesenteric taenia present. Two enlargements are seen, one on 



each side of the tube, caused by the presence of blood-vessels. It will be noted that the muscle here is in no way 



involved. 



arc indicated, and the other (that they are marked by "mesenchymal thickenings") 

 is wide of the point, Thickenings are found scattered along at irregular intervals; 

 these, upon cross-section, might be taken to indicate the developing taenia-, but 

 they do not involve the muscle in any way. Indeed, when the taeniae appear they 

 are quite distinct from these thickenings, which in reality are caused by large blood- 

 vessels (fig. 5). . 



At about 100 mm. there appear at two places in the muscle an accumulation of 

 fibers which cause a marked thickening in the layer (fig. 6). These masses are 

 crescentic in shape, resembling the mesenteric thickening, are located about equi- 

 distant from it and from each other, and extend the whole length of the bowel. 

 They are accumulations of muscle-fibers within the layer at these two places and 

 continue to enlarge until the 105-mm. stage, when they are distinctly formed and 

 fixed in their triangular position. When traced for some distance along the bowel 

 they are seen to vary in size and shape; at places they are broad and flat or narrow 



