MUSCULAR FIBRE. 557 



connecting the bundles of fibres together; in the gene- 

 rality of the fibrous tissues, the capillaries are not well 

 seen, except in that of the dura-mater and periosteum ; 

 in other parts it must be injected to show them. 



The yellow fibrous tissue 

 is highly elastic ; it consists 

 of bundles of fibres covered 

 with, and connected together 

 by, areolar tissue : the fibres 

 are of a yellow colour, some 

 round, others flattened ; 

 they are not always paral- 

 lel, but frequently bifurcate 

 and anastomose with neigh- 

 bouring fibres. It is always 

 difficult to separate the fibres 

 from each other ; and when 

 separated, the elasticity of Fig> ' 

 each individual fibre is shown 

 by its tendency to curl up at the end. The fibres in the 

 human subject vary in diameter from the 1 -5000th to 

 1-1 0,000th of an inch. Acetic acid of ordinary strength 

 does not act on yellow fibrous tissue ; nor for a very 

 long time after maceration in water or spirit does its 

 elasticity diminish. Very long boiling extracts from it a 

 minute quantity of a substance nearly allied to gelatine ; 

 neither nuclei nor a trace of a cell can be seen in it after 

 the addition of acetic acid: both are readily seen when 

 white fibrous element is treated with this acid. 



Muscular Fibre. There are three different kinds of 

 muscular fibre found in the animal body : 1st, in the 

 muscle of the skeleton ; 2d, in the muscle of the heart ; 

 and 3d, in the stomach, intestine, &c. The functions of 

 muscular fibre may be referred to two kinds voluntary 

 and involuntary. The muscles endowed with voluntary 

 power are those of the skeleton; the involuntary are those 

 of the heart, stomach, intestine, &c. 



Muscular fibre is held together by a very delicate tubular 

 sheath, nearly resembling simple structureless membrane. 

 This cannot always be discerned; but when the two ends 

 are drawn asunder, it will be perceived to rise up iii 



