.510 



MUSCLE. 



gularly one in front of the other, as a little 

 consideration will shew. Hence the latter 

 seldom seem so definite or regular as the 

 former. Nevertheless their union, seen on the 

 surface of a detached disc, often presents much 

 regularity, and forms curved or straight lines, 

 such as result when a number of balls of equal 

 size are huddled together on a level. 



It may be concluded from what has now 

 been advanced, that the discs and tibrillae, (or, 

 in other words, the general mass of the fibre,) 

 are made up of a number of particles, which 

 I have termed primitive particles, or sarcous 

 elements, and which would be obtained in a 

 detached form by a general separation occur- 

 ring along the transverse and longitudinal lines 

 visible in the fibre. The existence of these 

 particles, as well as their form and size, is in- 

 dicated in the structure of the fibre, while yet 

 entire; but they are united together, and have 

 no independent existence, each being by its 

 very nature a part of the mass, which is ren- 

 dered incomplete by the removal of a single 

 element. It results also from this descrip- 

 tion that these particles have no definite 

 outline on all their aspects, being united 

 together; and that they only obtain such an 

 outline on being severed ; on which account 

 it is perhaps impossible to say whether, in 

 the perfect fibre, they be rounded, square, or 

 polygonal. 



An example of the strong lateral union of 

 these particles to one another was presented by 

 the specimen from which the following sketch 

 was taken. It consisted of two or three ele- 

 mentary fibres from the leg of a newly-born 

 rabbit, which had been kept for some months 

 in weak spirit. They were lying in a curved 

 form on the fi^ld of the microscope, and pre- 

 sented on the convex edge transverse series of 

 Fig. 289. the particles, which, hav- 

 ing lost their longitudinal 

 while they retained their 

 lateral union, stood out in 

 relief, as represented in 

 fig. 289, a, a, a. 



It sometimes happens 

 that a linear series of them 

 (a fibrilla) is separated, 

 which has the appearance 

 of a necklace of beads, 

 with constricted intervals, 

 while at other times the 

 intervals, though dark, are 

 of equal width with the 

 light or highly refracting 

 particles. Again, it is pos- 

 sible, by steeping in acid 



a transverse section of a 

 In the intervals between , . , , 



the projecting parti-** muscle, to separate 

 cles, others 'have be- tne particles considerably 

 come detached. from one another, and to 



see that they are granules 

 acting as lenses, being much more refractive 

 than the material connecting them. Such 

 transverse sections are an artificial division 

 into discs, and the intervals between the par- 

 ticles widen out most in specimens taken from 

 birds (fig. 290). 



Fig. 290. 



Transverse section of three 

 elementary fibres of the 

 dried pectoral muscle of 

 the Teal, ( Querquedula 

 crecca,) treated with weak 

 citric acid, shewing the 

 round refracting particles 

 separated from one ano- 

 ther. The cut edge of the 

 tubular sheath of each fibre 

 is also seen. 



It is in these sarcous elements that the con- 

 tractile power resides, and, as they are apt to 

 retain after death the varying effects of the con- 

 traction they have undergone during the rigor 

 mortis, it is not easy to give an exact measure- 

 ment of their size or shape. An average drawn 

 from very numerous observations shews, how- 

 ever, that they are very nearly alike in these 

 respects in all animals and at all periods of life. 

 Their diameter in the longitudinal direction of 

 the fibre, as indicated by the distance between 

 the transverse lines, is thus shown to be :* 



No. of 

 Eng.Inch. Observations. 



In the Human subject. . 

 In Mammalia generally 



In Birds ............ 



In Reptiles .......... 



700 



In 



1T ' TM 



27 



15 



7 



7 



2 o 

 8 



Their diameter in the opposite direction or 

 that marked by the distance between the long- 

 itudinal lines is less, often by a half, but 

 liable to variety from the cause already spe- 

 cified. 



In a paper, entitled " On Fibre," read before 

 the Royal Society, on the 16th December and 

 the eth January last,f Dr. Barry describes the 

 fibrilla to be a flat filament rounded at the 

 edges, and deeply grooved along the middle 

 line on both its surfaces. He states that this 

 flat filament consists of two spiral threads 

 placed side by side, wit/i their coils interlacing : 

 that it " is so situated in the fasciculus (ele- 

 mentary fibre) of voluntary muscle, as to pre- 

 sent its edge to the observer;" and that the 

 curves of the spiral thread, then seen, seem to 

 have been the appearance that " suggested the 

 idea of longitudinal bead-like enlargements 

 producing the strise." In Dr. Barry's opinion 

 " the dark longitudinal stria? are spaces (pro- 

 bably occupied by a lubricating fluid) between 

 the edges of flat filaments, and the dark trans- 

 verse striae, rows of spaces between the curves 

 of the spiral threads," of which each flat fila- 

 ment consists. " In a postscript, the author 

 observes, that there are states of voluntary 

 muscle in which the" (doubly-spiral, flat,) "lon- 

 gitudinal filaments have no concern in the 

 production of the transverse striae, these stria? 

 being occasioned by the windings of spirals, 

 within which very minute bundles of longi- 



* Auct. loc cit. p. 474. 



t Proceedings of the Royal Society, No. 51. 



