MUSCULAR TISSUE. 



287 



Fig. 324. A BRANCHED 3IUS- 



CULAR FIBRE FROM THE 

 FROG'S TONGUE, MAGNIFIED 



350 DIAMETERS. (Kollikcr. ) 



either is fixed to a tendon, both extremities of the fibre terminate in the way 

 described, so that it has a long cylindrical shape, but when provided with tapering 

 .ends it becomes somewhat spindle-shaped. In some 

 jnuscles, e.g., the sartorius, fibres have been measured 

 which are much longer than the dimension above given. 



Generally speaking the fibres neither divide nor anas- 

 tomose ; but this rule is not without exception. In the 

 tongue of the frog the muscular fibres (fig. 324) as they 

 approach the surface divide into numerous branches, by 

 which they are attached to the under surface of the 

 mucous membrane (Kolliker). The same thing has also 

 been seen in the tongue of man and various animals : 

 and the fibres of the facial muscles of mammals divide 

 in a similar manner where they fix themselves to the 

 skin (Busk and Huxley). 



Structure of the fibres ; sarcolemma. A mus- 

 cular fibre may be said to consist of a soft substance 

 enclosed in a tubular sheath. The latter is named the 

 sarcolemma. It consists of transparent and apparently 

 homogeneous elastic membrane, and, being comparatively 

 tough, will sometimes remain entire when the included 

 muscular substance is ruptured, as represented in figs. 

 525, 326. It is especially well seen in fish and amphibia, 

 for in these it is thicker and stronger than in mammalian 

 muscle, in which it is more difficult to render evident but 

 nevertheless always exists (fig. 326). Nuclei are found 

 on the inner surface of the sarcolemma, but these belong 

 rather to the contractile substance than to the 

 inclosing membrane, and will be afterwards more 

 fully described. 



Muscular substance. When viewed by 

 transmitted light even with a comparatively low 

 power of the microscope, the fibres, which are 

 clear and pellucid in aspect, appear marked with 

 parallel stripes or bands alternately light and 

 dark passing across them with great regularity 

 (fig. 327), and this not only at the surface but, 



fig. 326. SARCOLEMMA OF MAMMALIAN MUSCLE, HIGHLY MAGNIFIED. (E. A. S.) 

 The fibre is represented at a place where the muscular substance has 

 tecome ruptured and has shrunk away, leaving the sarcolemma (with a nucleus 

 adhering to it) clear. The fibre had been treated with serum acidulated with 

 .acetic acid. 



.as may be seen by altering the focus of the microscope, through- 

 out its substance also. In a moderately extended fibre about 

 -eight or nine dark and as many light bands may be counted in 

 the length of yoVo f an i ncn > which would give about 17000 inch 

 as the breadth of each. But whilst this maybe assigned as 

 their usual breadth in human muscle, they are in different parts 

 found to be much narrower, so that not unfrequently there are 

 twice as many in the space mentioned. This closer approxima- 

 tion may generally be noticed in thicker and apparently 

 contracted parts of the fibre. The cross-striped appearance, which is very character- 

 istic, is found in all the skeletal muscles ; but it is not altogether confined 



Fig. 325. MUSCULAR FIBRE OF FISH, 

 SUBSTANCE OF FIBRE RDPTURED so 



AS TO EXHIBIT SARCOLEMMA. (After 



Bowman. ) 



