EBEN J. CAREY 



365 



The differentiation of the outer longitudinal muscle coat therefore 

 coincides, in time, with the rapid growth in length of the intestinal 

 epithelium. The inner smooth muscle coat, on the other hand, is 

 formed during the period of the rapid growth of the intestinal epi- 

 thehal tube in diameter. Once the formation of the inner circular 

 muscular rings is fairly established a resistance to growth in width is 



10 iZ ii^ ih 



is t/> ^jt z^ ze ig 30 3S- 3^ 36 ig 'ffi ^2 yy ^6 

 /.efyotf>o9 etfbrya in ^i/lrme/ers 



Fig. U. Curve representing the ratio of the diameter to the length of the de- 

 scending colon in embryos 10 to 45 mm. in length. Particular attention is di- 

 rected to the fact that in embryos 10 to 25 mm. in length the intestine grows rela- 

 tively more rapidly in diameter than in length. In embryos from 25 to 45 mm. in 

 length the intestine grows more rapidly in length than in diameter. The inner 

 circular smooth muscle is formed durmg the period of rapid growth of the intes- 

 tine in diameter. During the period of the rapid growth of the intestine in length 

 the histogenesis of the outer longitudinal smooth muscle coat is taking place. 



encountered by the cells surrounding the rapidly dilating lumen. 

 These cells then grow primarily along the path of least resistance in a 

 longitudinal manner. At this stage the longitudinal muscle cell, 

 spherical in shape (Fig. 12), is elongated to a spindle-shaped structure 

 (Fig. 13). 



An interesting correlation in the development of the esophagus in 

 man may be cited. This correlation was detected in the work of 



