STUDIES IN THE DYNAMICS OF HISTOGENESIS. 



II. Tension of Differential Growth as a Stimulus to 

 Myogenesis in the Esophagus. 



By EBEN J. CAREY. 



{From the Department of Anatomy, College of Medicine, Marquette University 



Milwaukee^ 



(Received for publication, April 3, 1920.) 

 introduction. 



Facts presented, for the first time, in a previous publication by 

 the writer (1919-20) prove that the developing descending colon of 

 the pig embryo possesses two zones of differential growth which by 

 their interaction mutually influence each other during the formation 

 period. The inner epithelial tube is the dominant, most active re- 

 gion of growth. It presents numerous mitotic figures which pursue a 

 path cephalad, primarily, in the manner of a left-handed helix. The 

 outer mesenchymal zone is less active in growth and early in develop- 

 ment is composed of a uniform mass of undifferentiated cells. 



The inner, rapidly growing, epithelial tube practically revolves due 

 to the rapid spiral growth of its cells. With subsequent growth an 

 apparent ring (this is qualified apparent for in reality a close spiral is 

 formed) of smooth muscle myoblasts appears gradually near the periph- 

 ery of the vortex. 



This position taken by the inner, close spiral, smooth muscle coat 

 at some distance from the epithelial tube is dependent upon an op- 

 timum tension. The attitude heretofore taken by embryologists 

 eliminated the search for the underlying cause of the first formed, 

 inner, muscle coat The theory of self-differentiation excluded in- 

 terpretation as regards myogenesis. A certain mesenchymal cell, re- 

 gardless of position, was considered as destined to become a myoblast. 



This highly differentiated tissue is now considered to self-develop, 

 for so called muscle-forming elements have been identified in the 



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