272 



OF MUSCULAR CONTRACTILITY, 



Fig. 61. 



Portion of Human Muscular Fibre, separating into disks, by cleavage in direction of transverse Striae. 

 After Bowman. 



series of discs, as shown in Fig. 61 [and Fig. 62]. This cleavage is just as 

 natural as the former, though less frequent ; and it leads us to a view of the 

 composition of Muscular Fibre, somewhat different from the one commonly 

 adopted. To use the words of Mr. Bowman,* it would be as proper to say, 

 "that the fibre is a pile of discs, as that it is. a bundle of fibrillx; but in fact 

 it is neither the one nor the other, but a mass in whose structure there is an 

 intimation of the existence of both, and a tendency to cleave in the two direc- 

 tions. If there were a general disintegration along all the lines in both direc- 

 tions, there would result a series of particles, which may be termed primitive 

 particles or sarcous elements, the union of which constitutes the mass of the 



[Fig. 62. 



7 8 



Fragments of Striped Elementary Fibres, showing a cleavage in opposite directions ; magnified 300 dia- 

 meters; 1, longitudinal cleavage ; the longitudinal and transverse lines are both seen; some longitudinal 

 lines are darker and wider than the rest, and are not continuous from end to end ; this results from par- 

 tial separation of the fibrillae; 6, fibrillee. separated from one another by violence at the broken end of the 

 fibre, and marked by transverse lines equal in width to those on the fibre; 7, & represent two appear- 

 ances commonly presented by the separated single fibrillae, (more highly magnified;) at 7 the borders and 

 transverse lines are all perfectly rectilinear, and the included spaces perfectly rectangular; at 8 the 

 borders are scalloped, the spaces bead-like; when most distinct and definite, the fibrilla presents the former 

 of these appearances: 2, transverse cleavage; the longitudinal lines are scarcely visible ; 3, incomplete 

 fracture following the opposite surfaces of a disc, which stretches across the interval and retains the two 

 fragments in connection ; the edge and surface of this disc are seen to be minutely granular, the granules 

 corresponding in size to the thickness of the disc, and to the distance between the faint longitudinal lines; 

 4, another disc nearly detached; 5, detached disc more highly magnified, showing the sarcous elements.] 



* See Bowman on the Minute Structure and Movements of Voluntary Muscle, in 

 Phil. Trans. 1840. His description is here followed by the Author, as that most gene- 

 rallyreceived amongst Physiologists. An entirely different account, however, has been 

 given by Dr. Barry (Phil. Trans. 1842). The Author cannot satisfy himself, that either 

 of these explains all the appearances which are presented by this interesting object. 



