VOLUNTARY MUSCLES. 451 



under the microscope is characteristic and unmistakable. 

 They present regular transverse striae, formed of alternating 

 dark and clear bands about 25 ^ 0() of an inch wide. These 

 are generally very distinct in healthy muscles. In addition 

 we frequently observe longitudinal striae, not so distinct, 

 and quite difficult to follow to any extent in the length of 

 the fasciculus, but tolerably well marked, particularly in 

 muscles that are habitually exercised. The muscular sub- 

 stance, presenting this peculiar striated appearance, is en- 

 closed in an excessively thin but elastic and resisting 

 tubular membrane, called the sarcolemma, or myolemma. 

 According to Robin, 1 the sarcolemma is composed of the 

 same substance as the elastic tissue. This envelope cannot 

 be seen in ordinary preparations of the muscular tissue ; but 

 it frequently happens that the contractile muscular sub- 

 stance is broken, leaving ths sarcolemma intact, which 

 gives a good view of the membrane and conveys an idea of 

 its strength and elasticity. Attached to the inner surface of 

 the sarcolemma, are numerous small, elongated nuclei with 

 their long diameter in the direction of the fasciculi. These 

 are not usually well seen in the unaltered muscle, but the 

 addition of acetic acid renders the muscular substance pale 

 and destroys the striae, when the nuclei become very 

 distinct. 



Water, after a time, acts upon the muscular tissue, ren- 

 dering the fasciculi somewhat paler and larger. Acetic acid 

 and alkaline solutions efface the striae, and the fibres become 

 semitransparent. 



In fasciculi that are slightly decomposed, there is fre- 

 quently a separation at the extremity into numerous smaller 

 fibres, called fibrillae. These, when isolated, present the same 

 striated appearance as the primitive fasciculus ; viz., alter- 

 nate dark and light portions. They measure about 2g ^ o6 

 of an inch in diameter, and their number, in the largest 

 primitive fibres, is estimated by Kolliker at about two thou- 



1 Loc. tit. 



