MUSCULAR TISSUE. 65 



delicate web called the " perimysium, " in contradistinction to the sheath of 

 areolar tissue which invests the entire muscle, the " epimysium." The bundles 

 are termed "fasciculi;" they are prismatic in shape, of different sizes in 

 different muscles, and for the most part placed parallel to one another, though 

 they have a tendency to converge toward their tendinous attachments. Each 

 fasciculus is made up of a bundle of fibres, which also run parallel with each 

 other, and which are separated from one another by 

 a delicate connective tissue derived from the peri- ? 



mysium, and termed cn<linii*(iim (Fig. 37). 



A muscular fibre may be said to consist of a soft 

 contractile substance enclosed in a tubular sheath, 

 named by Bowman the sarculiTiiinn. The fibres are 

 cylindrical or prismatic in shape, and are of no great 

 length, not extending, it is said, further than an inch 

 and a half. They end either by blending with the 

 tendon or aponeurosis, or else by becoming drawn 

 out into a tapering extremity which is connected to 

 the neighboring fibre by means of the sarcolemma. 

 Their breadth varies in man from -^^ to -g-^-g- of an 

 inch, the average of the majoritv being about -j-i-^. 



, = ' . FIG. 37. Transverse section irom 



As a rule, the fibres do not divide or anastomose: the sterno-mastoid in man. Magni- 



V 11 -n-i J.P-I fled 50 times, a. External perimys- 



but occasionally, especially m the tongue and facial ium. b. Fasciculus, c. internal 

 muscles, the fibres may be seen to divide into several P erim * 8ium - d - ^e. 

 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 the tissue of the tendon, 

 and prolonged more or less into the tendon, so that the latter forms a kind of 

 sheath around the fibre for a longer or shorter distance. When muscular fibres 

 are attached to the skin or mucous membranes, their sarcolemma probably 

 becomes continuous with the fibres 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. 38). On 

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

 the fibre in the lower animals, elongated nuclei are seen (Fig. 55), and in connec- 

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



L pon examination of a muscular fibre by transmitted light under a sufficiently 

 high power, it is found to be apparently marked by alternate light and dark bands 

 or strise. which pass transversely, or somewhat obliquely, round the fibre (Fig. 38). 

 The dark and light bands are of nearly equal breadth, and alternate with great regu- 

 larity. Other striae pass longitudinally over the fibres, though they are less distinct 

 than the former. This longitudinal striation gives the fibre the appearance of 

 being made up of a bundle of fibrilla?. The muscular fibre can be broken up either 

 in a longitudinal or transverse direction (Fig. 39). If hardened in alcohol, it can 

 be broken up longitudinally, and forms the so-called fibrillae of which some suppose 

 the fibre to be made up. Each fibril is marked by transverse striae, and appears 

 to consist of a single row of minute quadrangular particles, named " sarcous 

 elements " by Bowman. A still further division, however, is capable of being 

 made, and each of these fibrillse may be divided into minute threads (Fig. 40, B, d). 

 consisting of an alternate dark and light spot. After exposure to the action of 

 dilute hydrochloric acid, the muscular fibre can be broken transversely (Fig. 39, 

 B). It then forms disks or plates, consisting of the same quadrangular particles, 

 attached by their lateral surfaces. 



Upon closer examination with a very high power the appearances become 

 more complicated and are susceptible of various interpretations. The transverse 

 striation, which in Figs. 38 and 39 appears as a mere alternation of dark and 



