94 EBEN J. CAREY 



tube to grow more rapidly in a longitudinal direction than in a 

 transverse. The force of the growth of the inner tube during 

 the period of its rapid longitudinal extension, in embryos 30-50 

 mm. in length, exerts a longitudinal, spiral tension upon the 

 outer tube which had been retarded in growth. Concomitantly 

 with the epithelial tube's period of rapid growth in length, the 

 outer elongated spiral muscle coat is being derived from the 

 splanchnic mesoderm. 



According to the evidence, muscle formation in the gut is 

 not due to a self-differentiation, nor to a spontaneous self-elonga- 

 tion of the myoblast, but is a dependent modification of the 

 mesenchyme, due to the tension elicited by an extrinsic growth 

 force. In view of other evidence yet to be presented, the writer 

 is confident that this is the fact as regards all musculature. As 

 an example, we may cite the spiral direction of the cardiac 

 fasciculi corresponding to the changes in the vortical tension 

 caused by the helicoidal blood stream flowing through the 

 embryonic heart. In regard to the lingual musculature, an 

 extrinsic force is found in the accelerated growth of the ento- 

 dermal epithelium of the tongue. 



The facts of direct observation prove that the formation of 

 muscle tissue is a function of its position. Muscle tissue is 

 formed in situ and is dependent upon an optimum tension, 

 elicited by a dominant zone of accelerated growth, forcing by 

 traction a connected zone retarded in growth. The direction 

 of the resultant muscular fasciculi serves as a criterion of the 

 direction of the dominant accelerated force which exerted the 

 tension of differential growth. 



In view of the evidence supporting the conclusion, that muscles 

 arise through traction exerted upon the mesenchyme by a force 

 extrinsic to the zone of myogenesis, it is as logical to claim that 

 they self-elongate as it is to assert that a rubber band can stretch 

 itself or a balloon can self -dilate. In the latter cases extrinsic 

 forces are implied. As regards muscle origin, these forces are 

 elicited by extrinsic zones of accelerated growth, inevitably 

 drawing by traction retarded zones of growth, this being due 

 to their relative positions to each other. 



