492 PAUL E. LINEBACK 



place where the colon comes into relation with the duodenum. 

 In figure 8 the apex of the bend a is at I, of this distance, and 

 accordingly the flexures labelled a in the two figures may be 

 regarded as homologous. But in figure 9, a no longer marks the 

 apex. The bend which it designates has been incorporated in 

 the outer coil, together with the reversed bend h, and a new apex 

 appears at c (which may fairly be compared with c in figure 8). 

 Beyond this point, in figure 9, the proximal half of the colon 

 still pursues a zig-zag course as in earlier stages, but it swings 

 back and fourth through shorter arcs, and the transfer of the 

 apex from c to ^ is alrejidy suggested. To accomplish this, the 

 flexures d, e, and / are destined to pass through the condition 

 at present exhibited by a and h. In the 95-mm. embryo (fig. 

 10) this has taken place, and slight irregularities in the outer 

 coil are all that remain of the former to-and-fro oscillations. 



The outer or ascending spiral develops in advance' of the 

 inner, descending spiral, as may be seen in the figures already 

 examined. The coils in the distal half of the colon are quite 

 disorganized in figures 5 to 8. Beginning in figure 9 (at g) and 

 more extensively in figure 10, the apical portion of the ascend- 

 ing coil is accompanied by a descending coil, and thus the final 

 relation between the outer and inner coils is beginning to appear. 

 An apex is thus estabhshed which will not advance further by 

 taking up flexures in its path, but chiefly through elongation, 

 which it shares with the rest of the colon, and by becoming more 

 tightly wound about its axis. However, it will be shown that a 

 slight advance of the apex along the inner or descending limb 

 is yet to occur, at the time when the characteristic apical pat- 

 tern is produced. 



The final stages are shown in figures 11 to 14. In the embrj^o 

 of 110 mm. (fig. 11) three revolutions have been completed, and 

 except for the loosely wound apex, the spiral appears finished. ^ 

 The flexure a is destined to turn to the right and upward into the 

 concavity of the flexure c, and thus it will form the apical pat- 



^ The counting of the revolutions in the figures will be facilitated by placing 

 a straight edge from the ileo-colic junction to the apex. 



