MUSCULAR FIBRE. 611 



transparent; whilst the arrangement of the bloodvessels can only 

 be shown by means of injections ( 433). Fragments of the 

 tubules of the kidney, sometimes having the Malpighian cap- 

 sules in connection with them, may also be detached by scraping 

 its cut surface ; but the true relations of these parts can only be 

 shown by thin transparent sections, and by injections of the 

 bloodvessels and tubuli. The simple follicles contained in the 

 walls of the stomach are brought into view by vertical sections ; 

 but they may be still better examined by leaving small portions 

 of the lining membrane for a few days in dilute nitric acid (one 

 part to four of water), whereby the fibrous tissue will be so soft- 

 ened, that the clusters of glandular epithelium lining the cells 

 (which are but very little altered) will be readily separated. 



425. Muscular Tissue. Although we are accustomed to speak 

 of this tissue as consisting of "fibres," yet the ultimate struc- 

 ture of the "muscular fibre" is very different from that of the 

 simple fibrous tissues already described. When we examine an 

 ordinary Muscle (or piece of " flesh") with the naked eye, we 

 observe that it is made up of a number of fasciculi or bundles of 

 fibres ; which are arranged side by side with great regularity, in 

 the direction in which the muscle is to act; and which are 

 united by areolar tissue. These fasciculi may be separated into 

 smaller parts, which appear like simple fibres; but when these 

 are examined by the microscope, they are found to be them- 

 selves fasciculi, composed of minuter fibres bound together by 

 delicate filaments of areolar tissue. By carefully separating 

 these, we may obtain the ultimate " muscular fibre." This fibre 

 exists under two forms, the striated and the non-striated. The 

 former is chiefly distinguished by the transversely-striated ap- 

 pearance which it presents, and which is due to an alteration of 

 light and dark spaces along its whole extent ; the breadth and 

 distance of those striae vary, however, in different fibres, and 

 even in different parts of the same fibre, according to its state 

 of contraction or relaxation. Longitudinal striae are also fre- 

 quently visible, which are due to a partial separation between 

 the component fibrillse into which the fibre may be broken up. 

 When a fibre of this kind is more closely examined, it is seen to 

 consist of a delicate tubular sheath, quite distinct on the one 

 hand from the areolar tissue which binds the fibres into fasciculi, 

 and equally distinct from the internal substance of the fibre. 

 This membranous tube, which has been termed the myolemma, 

 is not perforated either by nerves or capillary vessels ; and forms, 

 in fact, a complete barrier between the real elements of Muscular 

 structure, and the surrounding parts. These elements appear to 

 be very minute cylindrical particles with flattened faces of nearly 

 uniform size, and adherent to each other both by their flat sur- 

 faces and by their edges. The former adhesion is usually the 

 most powerful; and causes the substance of the fibre, when it is 

 broken up, to present itself in the form of delicate fibriUce, each 



