514 



MUSCLE. 



indications of a regular arrangement in gra- 

 nules are usually to be met with. It is com- 

 mon for the longitudinal lines to become well- 

 defined before the transverse ones. When 

 both are strongly marked, as is always the case 

 at birth, the nuclei of the cells, which were 

 before visible, disappear, being shrouded from 

 view by the dark shadows caused by the mul- 

 titudinous refractions of the light transmitted 

 through the mass of granules; but, as before 

 stated, they can still be shown to exist by im- 

 mersion in a weak acid, which, while it swells 

 the fibrinous material of the granules and 

 obliterates their intervening lines, lias no action 

 upon the nuclei. 



b. Of the nnstriped elementary fibres. This 

 variety possesses far less interest than the other 

 in consequence of its apparent simplicity of 

 structure. The fibres consist of flattened bands, 

 generally of a pale colour, bulged at frequent 

 intervals by elongated corpuscles similar to 

 those of striped muscle, and capable of being 

 displayed by the same process (fig. 298). The 

 texture of these fibres seems to be homoge- 

 neous. By transmitted light they have usually 

 a soft, very finely mottled aspect, and without 

 a darkly-shaded border. Sometimes the mot- 

 tling is so decided as to appear granular, and 

 occasionally these granules are arranged in a 

 linear series for some distance. This condition 

 is probably an approximation towards the struc- 

 ture of the striped fibre, for I have observed 

 the granules to be about the size of the sarcous 

 elements already described. It is generally to 

 be seen more or less distinctly in the gizzard 

 of Birds, and I have now and then met with it in 

 the fresh muscle of the stomach, intestinal 

 canal, urinary bladder, and uterus of Mam- 

 malia. The ordinary diameter of the unstriped 



Fig. 298. 



Uiutriped elementary Jibres from the human colon. 



a, treated with acetic acid, and shewing the cor- 

 puscles. 



b, fragment of a detached fibre, not touched with 

 acid. 



fibre is from j^jth to ^th of an inch. From 

 this account of the appearance of these fibres, it 

 might be expected that their discrimination 

 from other tissues would be often difficult. 

 And, in fact, it is so to an inexperienced eye. 

 The peculiar texture, however, the size, the soft 

 margin, and, above all, the presence of nume- 

 rous elongated oval corpuscles, with two or 

 three granules in their centre, are characters 

 which, taken together, I believe to be decisive. 

 As a number of fibres usually take a parallel 

 course together, the bulgings occasioned by 

 the corpuscles give rise to partial longitudinal 

 shadows, extending for some way beyond the 

 corpuscles, in the intervals of the fibres. As 

 these irregular longitudinal shadows occur 

 pretty uniformly throughout an aggregation of 

 fibres, and as some are necessarily out of focus, 

 while others are in focus, the whole mass com- 

 monly presents a very confused reticulate ap- 

 pearance, which has given rise to an almost 

 universal notion that these fibres do, in reality, 

 interlace one with another, and do not run 

 parallel. This notion, however, is, in most 

 cases, erroneous. It is doubtful whether these 

 fibres are invested in a sarcolemma : none has 

 hitherto been detected in an unequivocal man- 

 ner. It is also still a matter of speculation 

 how they terminate, or whether they in all 

 instances have a termination. In the case of 

 the more or less circular set of fibres, inclosing 

 the small intestine, for example, it is uncertain 

 whether each fibre surrounds the canal once, 

 returning into itself as a ring, or, more than 

 once, as a spiral, or whether it passes only par- 

 tially round it, the rest of the circle being 

 completed by others. Whether the areolar 

 tissue (the representative of the fibrous) that 

 is always found in connection with these fibres, 

 serves to give them an attachment by union 

 with their extremities, or by involving them in 

 its meshes, is also altogether unknown. In 

 the gizzard of Birds the ends of the fibres are 

 united to white fibrous tissue, thus making an 

 approximation to the striped fibre, as they do 

 in colour. But I have not been able, after 

 diligent search, to detect the true transverse 

 stripes, which Ficinus describes to exist in this 

 organ. 



Of the mode of aggregation of the elemen- 

 tary fibres. The two kinds of fibre whose 

 structure has now been described, are aggre- 

 gated into masses of very various shape and 

 bulk, and supplied with areolar tissue, vessels 

 and nerves, so as together to form the organs 

 termed muscles. But if we trace these organs 

 downwards through the animal scale, we come 

 to examples in which solitary fibres exist with- 

 out any such appendages, and yet evidently 

 performing the office of, and truly constituting, 

 a perfect muscle. And even many fibres are 

 found, so far smaller than the usual dimen- 

 sions as to consist of only one or two linear 

 series of sarcous elements, and these perhaps 

 only visibly present near the centre of the fibre, 

 where developement is most advanced, and 

 the contractile energy greatest. In such minute 

 and simple forms we may perceive a transition 

 from the striped towards the unstriped fibre, 



