142 



MUSCULAR SYSTEM. 



[sect. 77. 



voluntary) muscular fibres, or 'primitive bundles (fig. 25) 



Fig. 63. 



• are 

 especially distinguished by their thickness and 

 the definite character of their component parts 

 from the most of the transversely-striped mus- 

 cular fibres occurring in other situations. With 

 respect to the latter distinction ; the sheath of 

 the primitive bundles, or the sarcolemma, is to 

 be recognised with facility in all bundles 

 without exception, particularly after the addi- 

 tion of water, acetic acid, and alkalies, and 

 also by maceration in diluted hydrochloric acid 

 {Bonders, Lehmann) , as a wholly structureless, 

 transparent, elastic, smooth investment, which, 

 in man, as well as in mammalia, is distin- 

 guished by its delicacy from the same part in 

 the lower vertebrate animals, especially the 

 naked amphibia. 



The muscular fibrils, or primitive fibrillar, 



fibre,™' primitive fasciculus, which are closely "invested by the sarcolemma, 

 ti/ormis); 600 times magni- may be isolated in muscles which have been 



fied. a. a small bundle; b. 

 an isolated fibril. 



or chromic acid. 



Fig. 64. 



macerated, or boiled, or preserved in alcohol 

 They are generally varicose, — i. e., marked at 

 intervals of 0-0004'" to 0001'", with 

 smaller or larger swellings ; and, as 

 their thicker and thinner places cor- 

 respond in position throughout the 

 whole thickness of the fibre, the 

 latter, for the most part, presents an 

 elegant transversely-striated aspect; 

 but, here and there, also a few fine 

 longitudinal strise; more rarely, from 

 the varicosities being faintly or not 

 at all expressed, the fibre may ex- 

 hibit only a longitudinal striation. 

 In the adult, the fibrillar do not sur- 

 round a central cavity or canal, but 

 form (fig. 64), with the scanty inter- 

 mediate counecting substance, perfectly compact fasciculi. On the 

 inner surface of the sarcolemma, numerous lenticular, or spindle- 

 shaped nuclei, are constantly found, of 0-003'" to 0-005"' in length, 

 and frequently furnished with nucleoli. These nuclei are not dis- 

 posed with any regularity: sometimes two or more at one level, or 



V 



A transverse section of some fibres from 

 the gastrocnemius of a man, 350 times 

 magnified, a. sarcolemma and interstitial 

 connective tissue; l>. section of the fibre 

 itself, showing many fatty granules im- 

 bedded in the interstices between the 

 fibrils. 



