CHAP. VII.] 



UNSTKIPED MUSCLE. 



159 



Fig. 46. 





posited, since their absolute number is far greater in the adult than 

 in the foetus, while their number relatively to the bulk of the fibre, 

 at these two epochs, remains nearly the same. 



Muscles grow by an increase, not: of the number, but of the bulk 

 of their elementary fibres : there is reason to believe that the num- 

 ber of fibres remains through life as it was in the foetus, and that 

 the spare or muscular build of the individual is determined by the 

 mould in which his body was originally cast. 



Of the Unstriped Fibres. This variety 

 possesses less interest than the other, in 

 consequence of the apparent simplicity of 

 its structure. The fibres consist of flat- 

 tened bands, generally of a pale colour, 

 bulged at frequent intervals by elongated 

 corpuscles, similar to those of striped mus- 

 cle, and capable of being displayed by the 

 same process.* The texture of these fibres w 

 seems to be homogeneous. By transmitted 

 light, they have usually a soft, very finely * 

 mottled aspect, and without a darkly- 

 shaded border. Sometimes the mottling 

 is so decided as to appear granular, 

 and occasionally these granules are ar- 

 ranged in a linear series for some distance. 

 This condition is probably an approach 

 towards the structure of the striped fibre, 

 for these granules are about the size of the 

 sarcous elements already described. It is J 00 ^ acid) 8howin e 





b. Corpuscles, or 



generally to be seen more or less distinctly shewin s their various appearances. 

 in the gizzards of birds ; and may be now 



and then met with in the fresh muscle of the stomach, intestinal 

 canal, urinary bladder, and uterus of mammalia. The ordinary 

 diameter of the unstriped fibre is from W^ to -r-xW of an inch. 



*- o O O I) 2000 



It might be expected, from this account of the appearance of 

 these fibres, that their discrimination from other tissues would be 

 often difficult. The peculiar texture, however, the size, the soft 

 margin, and, above all, the presence of numerous elongated oval cor- 

 puscles with two or three granules near their centre, are characters 

 which, when united, will seldom be mistaken. As a number of fibres 



* In some specimens, however, of both varieties of fibre, they may be dis- 



1 without tin- addition of an acid. 



