MUSCLE. 



[ 525 ] 



MUSCLE. 



Fig. 502. 



A, a primitive bundle, 

 magnified 350 diame- 



It often happens, especially when muscle 

 has been kept in spirit, that it separates trans- 

 versely into a number of flat disks (fig.^502) ; 

 hence it has been viewed as consisting of 

 these disks. Again, as 

 under certain conditions 

 it separates longitudi- 

 nally into fibrillae and 

 transversely into disks, 

 it has been supposed to 

 consist of primitive par- 

 ticles or * sarcous ele- 

 ments ' united end to 

 end as well as laterally. 

 We admit the existence 

 of the primitive fibrillse 

 as original components 

 of muscle, though there 

 can be little doubt that 

 the fibrillse are not ho- 

 mogeneous, and of uni- 

 form constitution either 

 chemical or physical. 

 On carefully examining 

 them at different foci, 

 it is seen that those por- 

 tions of isolated fibrils 



which appear dark when ters, partly separated 



the margins of the fibrils {J^ ^^ mo?e 



are best in focus, are magnified, end view. 



more highly refractive 

 than the intermediate portions, as shown 

 by the greater luminosity they acquire on 

 altering the focus of the object-glass; and 

 that this focal effect does not arise from a 

 lenticular form of the parts is evident from 

 the straight condition of the margins of the 

 fibrils. Hence these more highly refractive 

 parts probably constitute the proper mus- 

 cular substance, connected in the direction 

 of their length by a different kind of sub- 

 stance, which becomes brittle under the 

 action of spirit, whilst the former does not ; 

 for the line of separation into the disks 

 occurs through the less highly refractive 

 portions. And that these compound fibrils 

 naturally exist, is shown by their being dis- 

 tinguishable in a primitive bundle without 

 the use of reagents, or even of mechanical 

 means. 



It has always been supposed that the ulti- 

 mate fibrils are composed of cells arranged 

 end to end ; and the appearance represented 

 in PI. 22. fig. 36 a, which is sometimes met 

 with, might countenance this notion. But 

 whenever it is seen, there is imperfect defi- 

 nition, from the presence of too much liquid, 

 or some other cause; for we have never 



observed it when the object was properly 

 arranged and examined. 



On examining the tibrillse under a very 

 high power, each white band is seen to be 

 divided by a faint dark line, Krause's line or 

 membrane, which is regarded as a trans- 

 verse partition, the compartments being 

 occupied by the true muscular substance ; 

 and it is through this line, that the fibrils 

 separate into the disks (PI. 22. fig. 36 d) ; or, 

 often the same part appears bounded at each 

 end by a transverse dark line (fig. 36 b), or 

 both parts are traversed mesially by a trans- 

 verse dark line. In some instances we have 

 noticed a very delicate constriction, which 

 would account for these appearances; but 

 the explanation of this we have failed to 

 discover. 



The dark portions of the various fibrilL-e 

 of the primitive bundles being opposite to 

 each other, gives rise to the coarser dark 

 strise seen under a low power. But it often 

 happens that by pressure or manipulation 

 this natural relation is destroyed, the direc- 

 tion of the striae is altered, and sometimes 

 those of one bundle are made to alternate 

 with those of the next. Hence arises an 

 appearance of transverse or spiral fibres 

 (PL 22. fig. 35) ; but none such really exist 

 in muscle. 



Muscle consists chemically of a proteine 

 compound called syntonine, resembling 

 fibrine in many of its properties. By pressing 

 muscles a liquid is obtained, contaiuiDg some 

 peculiar organic substances. 



The unstriated and the striated muscular 

 fibres have the same chemical composition. 



In regard to the development of muscle, 

 it appears that muscular fibre proceeds from 

 cells which elongate, each becoming fusi- 

 form, and at the same time increasing enor- 

 mously in thickness; the nucleus also in- 

 creases, and the cell-contents become striated 

 to form the muscle. 



The muscles are very vascular. The 

 smaller branches of the vessels mostly run 

 parallel to the primitive bundles in the 

 perimysium, and anastomose by transverse 

 or oblique branches. 



The bundles of transversely striated mus- 

 cular fibres in many of the lower animals, 

 and in the heart of man, are found to branch 

 and form networks. This may be well 

 observed in the muscles of the tongue of 

 the frog. 



Schafer points out that the dark bands of 

 the muscular fibrils of certain insects, as 

 Dytiscus marginalis, are traversed by nume- 



