1108 



GENERAL ANATOMY OR HISTOLOGY. 



seen to divide into several branches. The precise mode in which the muscular 

 fibre joins the tendon has been variously described by different observers. It 

 may, perhaps, be sufficient to say that the sarcolemma, or membranous investment 

 of the muscular fibre, appears to become blended with a small bundle of fibres, 

 into which the tendon becomes subdivided, Avhile the muscular substance terminates 

 abruptly and can readily be made to retract from the point of junction. The are- 

 olar tissue between the fibres appears to be prolonged more or less into the tendon, 

 so as to form a kind of sheath around the tendon bundles for a longer or shorter 

 distance. When muscular fibres are attached to the skin or mucous membranes, 

 their fibres are described by Hyde Salter as becoming continuous with those of 

 the areolar tissue. 



The sarcolemma, or tubular sheath of the fibre, is a transparent, elastic, and 

 apparently homogeneous membrane of considerable toughness, so that it will some- 

 times remain entire when the included substance is ruptured (see Fig. 638). On 



FIG. 638. Two human muscular fibres. 

 Magnified 350 times. In the one, the bundle of 

 fibrillse (b) is torn, and the sarcolemma (a) is 

 seen as an empty tube. 



FIG. 639. Fragments of striped muscular fibres, 

 showing a cleavage in opposite directions. Magnified 

 300 diameters. A. Longitudinal cleavage. The longi- 

 tudinal and transverse lines are both seen. Some lon- 

 gitudinal lines are darker and wider than the rest, and 

 are not continuous from end to end. This results from 



Eartial separation of the fibrillse. c. Fibrillse separated 

 rom one another by violence at the broken end of the 

 fibre, and marked by transverse lines equal in width to 

 those on the fibre, c', c" represent two appearances com- 

 monly presented by the separated single fibrillse (more 

 highly magnified). At c' the borders and transverse lines 

 are all perfectly rectilinear, and the included spaces per- 

 fectly rectangular. At c" the borders are scalloped and 

 the s'paces bead-like. When most distinct and definite 

 the fibrilla presents the former of these appearances. 

 B. Transverse cleavage. The longitudinal lines are 

 scarcely visible, a. Incomplete fracture following the 

 opposite surfaces of a disk, which stretches across the 

 interval, and retains the two fragments in connection. 

 The edge and surfaces of this disk are seen to be 

 minutely granular, the granules corresponding in size 

 to the thickness of the disk and to the distance between 

 the faint longitudinal lines. 6. Another disk nearly- 

 detached, b'. Detached disk, more highly magnified, 

 showing the sarcous elements. 



the internal surface of the sarcolemma in mammalia, and also in the substance of 

 the fibre in the lower animals, elongated nuclei are seen, and in connection with 

 these a row of granules, apparently fatty, is sometimes observed. 



Upon examination of a voluntary muscular fibre by transmitted light, it is 

 found to be apparently marked by alternate light and dark bands or striae, which 

 pass transversely, or somewhat obliquely, round the fibre (Fig. 638). The dark 

 and light bands are of nearly equal breadth, and alternate with great regularity. 

 They vary in breadth from about y^r to yy^ of an inch. If the surface is 

 carefully focussed, rows of granules will be detected at the point of junction of 

 the dark and light bands, and very fine longitudinal lines may be seen running 

 through the dark bands and joining these granules together.' By treating the 

 specimen with certain reagents (e. g., chloride of gold) fine lines may be seen 

 running transversely between the granules, uniting them together. This appear- 

 ance is believed to be due to a reticulum or network of interstitial substance lying 

 between the contractile portions of the muscle. The longitudinal striation gives 



