

Fi s- 154 - 



Mass of Ultimate Fi- 



MUSCLES. 369 



as to have no marginal indentation on the surface; 

 thus constituting a uniform cylinder divided into 

 minute subdivisions by transverse septa, which are 

 formed by the adherent surfaces of contiguous cells. 

 The diameter of the fibril, in the state of relaxation, 

 is the 20,000th part of an inch. The cells are filled 

 with a transparent substance, to which Mr. Wilson 

 gives the name myoline^ and which differs in its re- 

 fractive density in different cells. In four consecu- 

 tive cells, the myoline is of greater density than 

 in the four succeeding cells, and this alternation is 

 repeated throughout the whole course of the fibril, bres from the Pectoraiis 

 In consequence of all the fibrils composing the ulti- ^\t f ^hi^^onuS" 

 mate fasciculus having the same structure ; and the These fibres have been 

 cells, which are in lateral juxtaposition, containing JSSri^acS* ^nd'Their 

 myoline of the same density, they act similarly on "numerous corpuscles, 

 light, and the whole presents to the eye of the mi- I* sLT'prese^fng 

 croscopic observer a succession of striae or bands, nucieoli," are shown. 

 dark and luminous alternately, and transverse to 

 the direction of the fasciculus; an appearance which has been noticed 

 by previous observers, but the cause of which, according to Mr. Wilson, 

 had not been before ascertained. A dark stria may occasionally ap- 

 pear as a luminous one, and conversely, when viewed by light trans- 

 mitted at different degrees of obliquity. The structure here described, 

 Mr. Wilson remarks, reduces the muscular fibre 

 to the simple type of organization exhibited in 

 the combination of a series of cells, associating 

 it with other tissues of cell formation; and may 

 probably, he thinks, open new sources of expla- 

 nation of the immediate agency of muscular 

 action, a power which, as he properly ob- 

 serves, is involved in the deepest mystery. 



One of the most recent views that have been 

 published, is that of Dr. Sharpey 1 and Dr. 

 Carpenter, 2 announced about the same time; 

 according to which, each of the alternate light 

 and dark particles of which the fibril is com- 

 posed, has a quadrilateral and generally a rec- 

 tangular form. Each bright particle or space 

 is marked across its centre by a fine, dark, 

 transverse line or shadow, by which the space 

 is divided into two equal parts; and, at times, 

 a bright border is perceptible on either side of 

 the fibril, so that each of the rectangular dark 

 bodies seems to be surrounded by a bright area, 

 having a similar quadrangular outline, as if 



Fig. 155. 



a An a p parently single fibril . 

 b - Longitudinal segment of a 



fibre consisting of a number of 



fibrils connected together. 



1 Human Anatomy, by Jones Quain, M. D., edited by Quain & Sharpey, Amer. edit., by 

 Leidy, i. 316, Philad., 1849. 



a Elements of Physiology, Amer. edit., p. 206, Philad., 1846. 



VOL. i. 24 



