530 



MOVEMENTS. 



fasciculi are from ^Vs to rsW of an mcn in diameter. In the adult, they measure from 



TTTF to yfa of an incn - 



The appearance of the primitive muscular fasciculi under the microscope is character- 

 tic and unmistakable. They present regular, transverse striaa, formed of alternating dark 

 and clear bands about ^^ of an inch wide. These are generally very distinct in healthy 

 muscles. In addition, we frequently observe longitudinal strias, 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 substance, present- 

 ing this peculiar striated appearance, is enclosed in an excessively thin but elastic and 

 resisting tubular membrane, called the sarcolemma or myolemma, which is probably 

 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 con- 

 tractile muscular substance is broken, leaving the 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 usually not well seen in the 

 unaltered muscle, but the addition of acetic acid renders the muscular substance pale and 

 destroys the stria3, when the nuclei become very distinct. 



Water, after a time, acts upon the muscular tissue, rendering 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 frequently a 

 separation at the extremity into numerous smaller fibres, called fibrillas. These, when 

 isolated, present the same striated appearance as the primitive fasciculus ; viz., alternate 

 dark and light portions. They measure about -^^-Q-Q of an inch in diameter, and their 

 number, in the largest primitive fibres, is estimated by Kolliker at about two thousand. 

 The structure of the fibrillae is probably uniform, the appearance of alternate dark and 

 light segments being due to dhTerences in thickness. In fact, it is well known that water, 

 by its simple mechanical action, swells the fibrillaa and causes the striss to disappear. 



Late researches have shown that the interior of each primitive fasciculus is pene- 

 trated by an excessively delicate membrane, closely surrounding the fibrillae. This 



arrangement may be distinctly seen in a 

 thin section of a fibre treated with a solu- 

 tion of salt in water in the proportion of 

 five parts per thousand. The arrangement 

 of this membrane, which is nothing more 

 nor less than a series of tubular sheaths 

 for the fibrillaa, is a strong argument in 

 favor of the view that the fibrilla is the ana- 

 tomical element of the muscular tissue. 



When we come to the question of the 

 real anatomical element of the muscular tis- 

 sue, there are only two reasonable views 

 that present themselves. One is that any 

 subdivision of the primitive fasciculus is arti- 

 ficial, and that it, with its investing mem- 

 brane, the sarcolemma, is the true element. 

 An argument in favor of this opinion is that 

 the tissue is most readily separated into fas- 

 ciculi, each enclosed in its own membrane 

 and not penetrated by vessels, nerves, or 

 lymphatics; while the fibrillse are situated 

 in a reticulum of canals, from which they cannot readily be isolated. The other opinion, 

 that the fibrillas are the ultimate elements, is based upon the fact that these little fibres 



inagn ijied 



FIG. 165. Voluntary muscular fibre, 

 250 diameters. (Sappey.) 



A, transverse strife and nuclei of a primitive fasciculus; 

 B, longitudinal striae and fibrillae of a primitive fas- 

 ciculus in which the sarcolemma has been lacerated 

 at one point by pressure. 



