342 THE SOLIDS. 



The fibrillae are, as already stated, included in a sheath, 

 the sarcoleinma of Bowman, both together constituting the 

 fibre. The sheath cannot at all times be seen : it may, however, 

 frequently be so, and especially when the fibrillae have been 

 torn across, the sheath at the same time not having been 

 divided, its greater elasticity enabling it to resist the force 

 which was sufficient to rupture the muscular fibrillae. It is in 

 such cases that the best view of this membrane is obtained. 

 (See Plate XLIL.,%. 1.) 



Treated with acetic acid, each fibre discloses most dis- 

 tinctly a considerable number of elongated and granular 

 nuclei, the outlines of which are in some cases visible, even 

 without the application of the acid. (See Plate XLIL 



fig- 2.) 



Of these nuclei, Mr. Bowman remarks : " In the fully 

 formed fibre if it be large, they lie at various depths within 

 it ; but if small, they are at or near the surface. They are 

 oval and flat, and of so little substance, that though many 

 times larger than the sarcous elements, and lying amongst 

 them, they do not interfere with their mutual apposition and 

 union." " It is doubtful whether the identical corpuscles, 

 originally present, remain through life, or whether successive 

 crops advance and decay during the progress of growth and 

 nutrition: but it is certain that as development proceeds 

 fresh corpuscles are deposited, 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 re- 

 mains nearly the same." * 



The above description is in part only correct. Thus I find, 

 first, that the nuclei are invariably situated on the external 

 surface of the fibre, the majority within the sheath, and either 

 adherent to this, or to the exterior fibrillae, some also being 

 placed on the outer surface of the sarcolemma ; facts which 

 throw much light upon the development of the muscular 

 fibre ; secondly, that the nuclei are not usually free nuclei, but 

 are contained in most cases in filaments in every way similar 



* Physiological Anatomy, vol. i. pp. 158, 159. 



