352 EBEN J. CAREY 



cross lines are solid in some locations, in others granular. No 

 intercallated discs, however, are seen. 



The transitional epithelium of the bladder has undergone a 

 hyperplasia (fig. 10). There are from ten to thirty layers of cells 

 in the vesicular epithelium. The inner cells are greatly flattened 

 and elongated in certain locations ; no nuclei are seen in the layer 

 bounding the lumen. In the greater part of the epithelium of the 

 bladder the cells are nucleated from the basal to the inner group of 

 cells. 



Bardeen ( '00- '07) and others have observed that the fibrillae 

 found in developed skeletal muscle at first show no cross-striations. 

 The deeply staining segment corresponds with the Q anisotropic 

 band of the adult fiber and the other with the I isotropic striation 

 (Warren Lewis, '12). The condition of the cross-striated bladder 

 muscle corresponds to the granular alignment which forms sub- 

 sequently the continuous Q bands illustrated during the develop- 

 ment of cross-striated muscle by Godlewski ( '02) . The vesicular 

 cross-striated fibers are formed from a syncytium composed of 

 endoplasmic nucleated units. This is comparable to the devel- 

 opmental observations of McGill ('07) and Godlewski ('02) for 

 smooth and striated muscles, respectively. 



DISCUSSION 



Tension of differential growth as a stimulus to myogenesis 



According to the embryological evidence (Carey, '21), muscle 

 formation in the gut is not due to a self-differentiation nor to a 

 spontaneous self-elongation 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 pre- 

 sented, the writer is confident that this is the fact as regards all 

 musculature. For 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 entodermal 

 epithelium of the tongue. 



