STUDIES ON THE LONGITUDINAL MUSCLE OF THE HUMAN COLON. 



37 



The entire collection was placed at my disposal through the generosity of 

 Professor Streeter, and I wish at this time to express my sincerest gratitude to him 

 for this great kindness. I wish also to express my indebtedness to Professor F. T. 

 Lewis and Professor R. R. Bensley for encouragement and material aid, and to recall 

 the delightful associations of their laboratories. 



Home experimentation was done on the 

 caecum of the guinea-pig, as this is a relatively 

 large structure with an especially well-developed 

 group of taenia?. A number of skiagrams were 

 examined and a few fluoroscopic inspections 

 were made of the human colon in the living state. 



DISCUSSION. 



The production of taeniae may be divided into two phases, each dependent upon 

 separate factors and attended by different phenomena: an early growth phase, 

 characterized by the appearance of the bands and their growth up to a fixed state, 

 and a functional phase, wherein the taeniae are accentuated and become especially 

 distinct through the functioning of the sacculations. 



The growth phase may be introduced by a brief consideration of the circular 

 muscle. The study of a closely graded series of embryos reveals the circular muscle 

 appearing much earlier than the longitudinal. This is true in the small intestine 

 as well as in the large. It is also found 

 that the muscle is first seen in the caudal 

 end of the intestine, and that it can sub- 

 sequently be traced throughout the entire 

 length of the latter. Lewis states that " at 42 

 mm. it is found throughout the colon," with 

 which my findings agree, although I should 

 conclude that it reaches that state of com- 

 pleteness somewhat earlier. Fetus No. 75 

 C. C, 30 mm. (fig. 1), shows it only in the 

 pelvic portion of the intestine; while in a 

 35-mm. specimen, No. 210 C. C, it can be 

 seen throughout the entire length of the 

 intestine. Evidently, its growth is upward from the caudal end of the tube and is 

 quite rapid. These items are significant, in that they show that in its manner of 

 growth the circular muscle exactly precedes the longitudinal, both in time of appear- 

 ance and time of completion. 



The zone just outside of the circular muscle is occupied by the myenteric 

 plexus, capillaries, and embryonic cells. The plexus occupies almost the entire 

 zone and is contained in rather poorly defined rounded and oval compartments, 

 which become very distinct by the 50-mm. stage. It is on the outside of these, and 

 in the angles between them, that the longitudinal muscle-fibers will make their 



Fig. 1. — Sagittal section of a human embryo 30 mm. 

 C R. length (No. 75, Carnegie Collection), showing 

 the circular muscle-fibers in the pelvic portion of the 

 colon. No longitudinal fibers are present. 



