MUSCLE. 



296. 



Trichinae within the sarcolemma, from which all the 



contractile material had disappeared. 



From an Eel. 



a, ovum. 



b, worms in slow motion. 



velopment, united to form a single tube, tlie 

 sepUi at first resulting from their apposition 

 having been absorbed. Tins opinion is un- 

 doubtedly ingenious ; but, as 1 have yet no 

 data from which to judge of its correctness, 

 I neither admit, nor deny it. I have seen 

 the sarcolemma in human muscle as early 

 as the period of birth, and have traced it at 

 all epochs, to old age, when the atrophy of 

 its contents has often seemed to render it 

 more easy of detection. It also remains in 

 muscles wasted by disease or accident at other 

 periods of life, and no difference appears to 

 occur in it whether the specimens examined 

 are pale or dark -coloured, firm or flaccid. It 

 is thickest in those classes that possess the 

 thickest elementary fibres, viz. in Crustacea 

 and Fish, and so thin in Birds, whose fibres 

 are the smallest, that it is often difficult to 

 detect it at all. 



With regard to the use which this singular 

 structure may serve in the economy of the 

 organ, our present ignorance of the manner in 

 which motion is excited renders any explana- 

 tion that might be offered of doubtful value. 

 But it has appeared probable to me, first, that 

 it may act as a mechanical protector and iso- 

 lator of the contractile tissue enclosed within it; 

 secondly, that its exquisitely smooth external 

 surface may facilitate those rapid minute 

 motions of neighbouring fibres, one against 

 another, which may be shown to occur in 

 contracting muscle (see MUSCULAR MOTION); 

 and, thirdly, that from its apparent similarity 

 in structure to the membrane of the nervous 

 tubules, which run among the fibres, and be- 

 tween which and the proper contractile tissue 

 it seems certainly to intervene, as well as 

 from its extensive contact and union with 

 the surface of the contractile tissue, it may be 

 the conducting medium of that influence, 

 whose mode of propagation the late disco- 

 very of the loop-like termination of the nerves 

 in muscle has hitherto only seemed to render 

 more inexplicable than ever. 



8. Of' the extremities of the elementary 

 fibres, and their attachment to other struc- 

 tures. Every fibre is fixed to fibrous tissue, or 

 to something analogous to it; but an accurate 

 examination of this difficult subject gives no 

 countenance to the ordinarily received opinion 

 that this tissue is prolonged over the whole fibre 

 from end to end, as its cellular sheath ; nor is 

 this view reconcileable with the physical require- 

 ments of the case. After many trials I have 

 never succeeded in isolating a muscular fibre 

 with the tendinous fibrillae pertaining to it, in 

 either Mammalia or Birds ; but this may be 



VOL. III. 



occasionally accomplished in Fishes, and in 

 certain muscles of insects. In these examples 

 the minute detachment of the fibrous tissue 

 may be seen to pass and become attached to 

 the truncated extremity of the fibre. The fibre 

 ends by a perfect disc, and with the whole 

 surface of this disc the tendon is connected 

 and continuous (fig. 297). The sarcolemma 



Fig. 297. 



Extremity of an elementary fibre, from the S/tate 

 ( Raia Batus), shewing its attachment to tendon. 



a, a, line of union between the two structures. 



b, tendon. 

 i p , muscle. 



ceases abruptly at the circumference of the 

 terminal disc, and here some small part of the 

 tendinous material appears to be joined to it. 

 The same disposition may be well seen in the 

 legs of certain insects (fig. 293). In other 

 cases, where the mustle is fixed obliquely to 

 a membranous surface, each fibre is obliquely 

 truncated at its extremity, at an angle deter- 

 mined by the inclination of its axis, instances 

 of which may be seen in the limbs of Crus- 

 tacea, and elsewhere. 



9. Development.- Theresearches of Valentin 

 and Schwann have shewn that a muscle con- 

 sists in the earliest stage of a mass of nu- 

 cleated cells, which first arrange themselves in 

 a linear series, with more or less regularity, 

 and then unite to constitute the elementary 

 fibres. As this process of agglutination of the 

 cells is going forward, a deposit of contractile 

 material gradually takes place within them, 

 commencing on the inner surface and ad- 

 vancing towards the centre, till the whole is 

 solidified. The deposition occurs in granules, 

 which, as they come into view, are seen to be 

 disposed in the utmost order, according to the 

 two directions already so often mentioned. 

 These granules are the sarcoits elements, and 

 being of the same size as in the perfect muscle, 

 the transverse stripes resulting from their appo- 

 sition are of the same width as in the adult; 

 but as they are very few in number, the fibres 

 which they compose are of corresponding 

 tenuity. From the very first period of their for- 

 mation these granules are parts of a mass and 

 not independent of one another, for as soon 

 as solid matter is deposited in the cells, faint 



2 L 



