MUSCLE. 343 



to those of unstriped muscle, and with which they are iden- 

 tical. 



Were the nuclei really scattered throughout the substance 

 of a muscular fibre, they would infallibly destroy the paral- 

 lelism of the striae, and greatly interfere with its contractile 

 power. 



The interpretation to be given of the location of the nuclei 

 and fibres of unstriped muscle in the situations indicated 

 will be explained when the subject of the development of 

 muscular fibre is considered ; at the same time, also, the point 

 raised by Mr. Bowman as to the persistence of the nuclei will 

 be discussed. 



The fibres of the upper part of the esophagus are striped 

 while those of the lower half are unstriped. It has been 

 considered a matter of uncertainty whether the two pass by 

 insensible gradations of structure into each other, or whether 

 they terminate abruptly. I believe, after careful examination, 

 that the latter supposition is the correct one. 



With a few remarks upon the peculiar views entertained 

 by Mr. Bowman, in reference to the structure of the striated 

 muscular fibre, the discussion of the structure of muscle may 

 be brought to a conclusion. 



" It was customary," writes Mr. Bowman *, " both before 

 and since his time (the time of Fontana), as at the present 

 day, to regard the fibre as a bundle of smaller ones, whence 

 the term primitive fasciculus, first given to it by him, and 

 adopted by Miiller : but this view of ihe subject is imper- 

 fect. The fibre always presents, upon and within it, longi- 

 tudinal dark lines, along which it will generally split up into 

 fibrillae ; but it is by a fracture alone that such fibrillae are 

 obtained. They do not exist as such in the fibre. And 

 further, it occasionally happens that no disposition whatever 

 is shown to the longitudinal cleavage ; but that, on the con- 

 trary, violence causes a separation along the transverse dark 

 lines, which always intersect the fibre in a plane perpen- 

 dicular to its axis. By such cleavage discs, and not fibrillae, 



* Physiological Anatomy, vol. i. pp. 151, 152. 

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