EBEN J. CAREY 



363 



As this concentric initial smooth muscle layer becomes differenti- 

 ated it tends to restrict the diametrical growth of the epithehal tube. 

 The epithelial mitotic figures under this restriction shift their planes 

 of division from a right angle to a parallel position with the smooth 

 muscle cells. This shifting results in an elongation of the intestine. 



TABLE II. 



Ratio of Diameter to Length of Entire Colon. 



In embryos 25 to 40 mm, (Tables I and II) in length, the elongation 

 of the descending colon is more rapid in growth than that of the 

 diameter. It is during this period that the outer longitudinal muscu- 

 lar coat is in the process of formation. The rapid growth of the epi- 

 thelial tube in length tends to elongate the peripheral undifferentiated 

 mesenchymal cells which were not directly involved in the formation 

 of the inner smooth muscular coat (Fig. 11). 



