488 PAUL E. LINEBACK 



The formation of coils in the large intestine begins in pig 

 embryos of about 30 mm. At 35 mm. (fig. 4), they are well 

 developed and are gathered in a knot between the caecum and 

 the splenic flexure. This flexure it should be noted, is the only 

 one which is found in the pig, so that the pig's ascending colon 

 corresponds with both the ascending and transverse colons of 

 human anatomy. A sinuous condition, preceding the formation 

 of distinct coils, is seen in the 30-mm. embryo, figure 3. Simi- 

 larly MacCallum found coils of the colon in pigs of 30 and 32 

 mm., and at 40 mm. he states that they 'form a conspicuous 

 mass.' 



The transformation of the mass of coils into the well-arranged 

 spiral of the adult may be followed in special dissections, and 

 from a large number of such preparations ten have been chosen 

 for illustration (figs. 5 to- 14). The final condition is shown in 

 figure 14, representing the colon from an adult, and this is pre- 

 ceded by a figure of the spiral foiu' weeks after birth (fig. 13). 

 The other drawings are from embryos ranging from 50-120 mm. 

 Throughout the series, the small intestines have been cut away 

 near the colic valve, but in figures 5 to 11 a short piece of the 

 ascending portion of the duodenum has been retained for orien- 

 tation. Around this the colon makes a characteristic bend, and 

 then, at the splenic flexure, it becomes the descending colon, 

 which is free from coils or kinks even in the adult. In all the 

 dissections the rectum has been cut away, and the entire mesen- 

 tery has been removed. The coils of the colon have separp.ted 

 from one another, but only so far as necessary to show the 

 course of the tube. This necessitates a slight displacement of 

 some of the flexures, but none has been omitted or radically 

 altered. 



In order to understand the stages in embryonic development 

 included in this series, it is necessary to have in mind certain 

 features of the condition to be finally attained, which are pre- 

 sented in figures 15 to 19. The apical portion of the coil in the 

 adult (fig. 14), and likewise in the more advanced embryos, pre- 

 sents the curious pattern shown in figure 15 (from an embryo of 

 200 mm.). The observer will be uncertain whether the point a 



