MUSCLE. 



[ 446 ] 



MUSCLE. 



of these disks. Again, as under certain con- 

 ditions it separates longitudinally into fibrillae 

 and transversely into disks, it has been sup- 

 posed to consist of * primitive particles ' or 

 ' sarcous elements' united end to end as well 

 as laterally. We admit the existence of the 

 primitive fibrillae as original components of 

 muscle, although there can be little doubt 

 that the fibrillae are not homogeneous, and 

 of uniform constitution either chemical or 

 physical. On carefully examining them at 

 different foci, it is seen that those portions 

 of isolated fibrils which appear dark when 

 the margins of the fibrils are best in focus, 

 are more highty refractive than the interme- 

 diate portions, as shown by the greater lu- 

 minosity 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 con- 

 stitute the proper muscular substance, con- 

 nected in the direction of their length by a 

 different kind of substance, which becomes 

 brittle under the action of spirit, whilst the 

 former does not so ; for the line of separa- 

 tion into the disks occurs through the less 

 highly refractive portions. And that these 

 compound fibrils naturally exist is shown by 

 their being distinguishable in a primitive 

 bundle without the use of reagents, or even 

 of mechanical means. 



It has also been supposed that the ulti- 

 mate fibrils are composed of cells arranged 

 end to end, and the appearance represented 

 in PI. 17. fig. 36 «, 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 ob- 

 served it when the object was properly ar- 

 ranged and examined. 



There are other appearances exhibited by 

 the fibrillae which cannot at present be satis- 

 factorily explained. Thus, sometimes each 

 more highly refractive portion is divided by 

 a dark line, indicating less refraction at that 

 part (PI. 17. fig. 36 c?, taken at the elevated 

 focus) ; at others the same part appears 

 bounded at each end by a transverse dark 

 line (fig. 36 h), or both parts are traversed 

 mesially by a transverse dark line. In some 

 instances we have noticed a very delicate 

 constriction, which would account for these 

 appearances, but the indication of this we 

 have failed to discover. 



The dark portions of the various fibrillae 



of the primitive bundles being opposite to 

 each other, gives rise to the coarser dark 

 striae seen under a lov/ power. But it often 

 happens that by pressure or manipulation 

 this natural relation is destroyed, the direc- 

 tion of the striae 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 (PI. 

 1/. fig. 35), but none such really exist in 

 muscle. 



The proper substance of muscle consists 

 chemically of a proteine compound called 

 syntonine, resembling fibrine in several of 

 its pro])erties, but differing from it in the 

 greater action of dilute muriatic acid, &c. 

 By pressing muscle, a liquid is obtained 

 containing some peculiar organic substances. 

 This liquid probably exists between the 

 fibrillae. 



The unstriated and the striated muscular 

 fibres have the same chemical composition. 



In regard to the development of muscle, 

 in its earliest stage it consists of nucleated 

 cells ; these become fusiform, arranged in 

 rows, and uniting by their ends, form fibres. 

 The proper muscular substance is then 

 formed within them, as a secondary deposit, 

 from the inner surface of the cells towards 

 the centre, until the whole is solidified. 



The muscles are very vascular. The 

 smaller branches of the vessels mostly run 

 parallel to the primitive bundles in the peri- 

 mysium, and anastomose by transverse or 

 oblique branches. 



They are also well supplied with nerves ; 

 these mostly terminate in a plexus of looped 

 branches (fig. 507). 



Muscle undergoes important changes in 

 disease. Wounds are filled up with areolar 

 or tendinous tissue. In atrophy and fatty 

 degeneration, the bundles become smaller, 

 softer, more readily broken up, the trans- 

 verse striae and fibrillae indistinct, or appa- 

 rently absent, and contain yellowish or brown 

 pigment-granules, with more or less nume- 

 rous globules of fat (PI. 30. fig. 14 a), and 

 sometimes a large number of nuclei or small 

 cells. 



The interfascicular areolar tissue is also 

 sometimes increased in amount, and fatty 

 tissue developed in it. Sometimes the mus- 

 cular substance is partially absorbed, and 

 the sarcolemma contracting, gives the bun- 

 dles a moniliform appearance (PI. 30. fig. 

 14 h). In tetanus, the fibres become vari- 

 cose and often ruptured, and the striae closer. 



The muscular tissue of the lower Verte- 



