304 



OF THE PRIMARY TISSUES OF THE HUMAN BODY. 



one another in size ; and contain an equal number of particles. The same par- 

 ticles compose both. To detach an entire fibrilla, is to abstract a particle of 

 every disk ; and vice versd." 



Fig. 91. 



Fig. 92. 



Muscular Fibre broken across, showing the un 

 torn Mydemma connecting the fragments. 



Portion of Striated Muscular Fibre separating into disks, by cleavage in direction of Transverse striae. 



299. The elements of Muscular Fibre are bound together, in the perfect con- 

 dition of the fibre, by a very delicate tubular sheath. This cannot always be 

 readily brought into view ; but it is occasionally seen with great distinctness : thus, 

 when the two ends of the fibre are drawn apart, its contents will sometimes 

 separate without the rupture of the sheath, which then becomes evident (Fig. 92) ; 

 and this, during the act of contraction, may sometimes be observed to rise up in 



wrinkles upon the surface of the fibre, as 

 seen in Fig. 96. This sheath is quite 

 distinct from the areolar tissue, which 

 binds the fibres into fasciculi ; and it has 

 been termed, for the sake of distinction, 

 the Myolemma. Its existence may be 

 demonstrated in any Muscular fibre, by 

 subjecting it to the action of fluids which 

 occasion a swelling of its contents ; this 

 is especially the effect of acids and alkalies, and may be well produced by the 

 citric and tartaric acids, and by potash. For a time, the Myolemma yields to 

 the distension which takes place from within ; but at last it bursts at particular 

 points, and a sort of hernia of its contents takes place, making the existence of 

 a perfect envelop in all other parts quite evident. This membrane is itself 

 perfectly transparent, and has nothing to do with the production of either the 

 longitudinal or the transverse striae. There is no reason to believe that it is 

 perforated either by nerves or by capillary vessels ; in fact, it seems to be an 

 effectual barrier between the real elements of Muscular structure, and the sur- 

 rounding parts. That it has no share in the contraction of the fibre, is evident 

 from the fact just mentioned, respecting the condition which it occasionally pre- 

 sents when the fibre is much shortened. 



300. Muscular Fibres are commonly described as cylindrical; but there is 

 reason to believe that they are rather of a polygonal form, their sides being 

 flattened against those of adjoining fibres (Fig. 93). In some instances the angles 

 are sharp and decided; in others they are rounded off, so as to leave spaces be- 

 tween the contiguous fibres for the passage of vessels. The average diameter of 

 the fibres in Man is stated by Mr. Bowman (loc. cit.) at about l-400th of an 

 inch ; being about l-352d of an inch in the male, and l-454th of an inch in 

 the female. He has met with extremes, however, as wide apart as l-507th and 

 l-192d of an inch in the male ; and 1-61 5th and l-384th of an inch in the 

 female. The average distance between the strise is about l-9400th of an inch; 

 but it is sometimes only l-15,000th, and sometimes as much as l-6000th, vary- 



