5 2 



TEXT-BOOK OF PHYSIOLOGY 



ment; the tendon is the inactive region, the passive transmitter of the 

 movement to the bones. 



A skeletal muscle is a complex organ consisting of a framework of 

 connective tissue, supporting muscle-fibers, blood-vessels, nerves, and 

 lymphatics. The general body of the muscle is covered by a dense layer 

 of connective tissue, the epimysium, which blends with and partly forms 

 the tendon. From the under surface of this covering, septa of connective 

 tissue pass inward, dividing and grouping the fibers into larger and smaller 

 bundles, termed fasciculi. The fasciculi, invested by a special sheath, the 

 perimysium, are prismatic in shape and on cross-section present an irregular 

 outline. The muscle-fibers composing the fasciculi are separated one from 

 another and supported by a very delicate connective tissue, the endomysium. 

 The connective tissue thus surrounding and penetrating the muscle binds 



the fibers into a distinct organ and 

 affords support to all remaining struc- 

 tures (Fig. 14). 



Histology of the Skeletal Mus- 

 cle-fiber. The muscle-fiber is the 

 ultimate anatomic unit of the muscle 

 system. The fibers for the most part 

 are arranged parallel one to another 

 and in a direction corresponding to 

 the long axis of the muscle. They 

 vary in length from 30 to 40 millimeters 

 and in breadth from 20 to 30 micro- 

 millimeters. There are exceptional 

 fibers, however, which have a much 

 greater length. As the fibers have 

 but a limited length in the vast major- 

 ity of muscles, each end, more or less 

 pointed or beveled, is united to adjoin- 

 ing fibers by cement. In this way the 

 length of the muscles is built up. 



When examined with the micro- 

 scope, the muscle-fiber is seen to be 

 cylindric or prismatic in shape and 

 to consist of a thin transparent mem- 

 brane, the sarcolemma, in which is 

 contained the true muscle substance or sarcous substance. The sarco- 

 lemma is elastic and adapts itself to all changes of form the sarcous sub- 

 stance undergoes. Beneath the sarcolemma there are several nuclei 

 surrounded by granular material; a muscle-fiber may therefore be re- 

 garded as a large multinucleated cell. Each fiber also presents a series 

 of transverse bands alternately dim and bright which give to it a striated 

 appearance. If the bright bands are examined with high magnifying 

 powers, each one is seen to be crossed by a fine dark line which at the 

 time of its discovery by Krause was regarded as the optic expression of a 

 membrane attached laterally to the sarcolemma. According to Rollet, 

 it is composed of a series of granules so closely applied as to give rise to the 

 appearance of a continuous line (Fig. 15). 



FIG. 14. FROM A CROSS-SECTION OF THE 

 ADDUCTOR MUSCLE OF A RABBIT. P. Peri- 

 mysium, containing two blood-vessels, at g; 

 m, muscle-fibers; many are shrunken and be- 

 tween them the endomysium, p, can be seen; 

 at x the section of muscle-fiber has fallen out. 

 X te. 



