STRUCTURE OF MUSCULAR TISSUE. 303 



linear direction, than it is in the production of capillaries ; the anastomoses of 

 the/ormer, in their complete state, being much more rare than that of the latter. 



6. Of the Muscular Tissue. 



297. The Muscular tissue, which is the instrument of the performance of all 

 the sensible movements of the body, exists under two forms; the ultimate fibres 

 being marked in one by transverse and longitudinal striae ; whilst in the other 

 they are plain, smooth, or unstriped. The former is chiefly concerned in the 

 various movements which are effected through the agency of the Nervous system, 

 and which are connected with the peculiarly Animal powers of the being. The 

 latter is with difficulty called into action through the nervous system, but is 

 much more readily excited by stimuli applied to itself; and this is employed to 

 perform various movements, which are more immediately concerned in the Yfege- 

 tative or Organic functions. By some, the two forms of tissue have been spoken 

 of as those of " voluntary" and of "involuntary" muscle : but this distinction is 

 not correct ; since every muscle ordinarily termed voluntary may be called into 

 action involuntarily, and the Heart, which is a purely " involuntary" muscle, 

 has the striated fibre characteristic of the " voluntary." 



298. When we examine an ordinary Muscle (from one of the extremities, for 

 example,) with the naked eye, we observe that it presents a fibrous appearance ; 

 and that the fibres are arranged with great regularity, in the direction in which 

 the muscle is to act. Upon further examination it is found, that these fibres are 

 arranged in fasciculi or bundles of larger or smaller size, connected by means of 

 areolar tissue ; and when the Microscope is applied to the smallest fibre which 

 can be seen with the naked eye, it is seen itself to consist of a fasciculus, com- 

 posed of a number of cylindrical fibres lying in a parallel direction, and closely 

 bound together. These primitive fibres present two sets of markings or stride ; 

 one set longitudinal, the other transverse or annular. By more closely ex- 

 amining these fibres when separated from each other, it is frequently seen that 

 each may be resolved into fibrittae, by the 



splitting of its contents in a longitudinal Fig- 90. 



direction, as shown in Fig. 90. These fibril- 



Ise have a peculiar beaded appearance, which 



will be presently noticed more particularly. 



It not unfrequently happens, however, 



that when a fibre is drawn apart, its contents 



separate in the direction of the transverse 



striae ; forming a series of disks, as shown in 



Fig. 91. This cleavage is just as natural as 



the former, though less frequent ; and it leads 



. 7 Vj3 \ . , T/T i Fasciculus of Striated Muscular Fibres ; the 



US tO a View Of the Composition Of MuSCUlar fibresseparatedatoneendintobrush-likebun- 



Fibre, somewhat different from the one com- dies offibrma;. 

 monly adopted. To use the words of Mr. 



Bowman, 1 it would be as proper to say "that the fibre is a pile of disks, as that 

 it is a bundle of jibrillae ; 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 directions. If there were a general disintegration along all 

 the lines in both directions, 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 fibre. These elementary particles are arranged and united together 

 in the two directions. All the resulting disks, as well as fibrillae, are equal to 



1 "On the Minute Structure and Movements of Voluntary Muscle," in "Philosophical 

 Transaction," 1840. 



