110 



MUSCULAR TISSUE. 



Fi.ir. 66. 



B 



tri" ! 



! 



'«38 



Ma/ 



but by the ktter arrangement the extent of motion is greater, for the 

 points of attachment are moved through a longer space. 



Fibres ; their figure and measurement. — In shape the fibres are 

 cylindrical, or prismatic, and in the latter case often with romided 

 surfaces and angles. Their size is tolerably uniform, although fibres 

 occur here and there in a muscle which differ greatly in size from the 

 prevailing standard. Bowman gave the average diameter in the male 

 at -j-i-TT and in the female at -^-J^^ of an inch. ""According to later mea- 

 surements by Kolliker in different regions of the body, the prevailing 

 size of the fibres in the muscles of the trunk and limbs is from -^^-^ to 

 4^0 of an inch, but is less in those of the head, especially in the facial 

 muscles, in which he found the diameter to range from -J „ down to 

 ^r^TTo of an inch. 

 Cross stripes. — When viewed by transmitted light with a suffi- 

 ciently high power of 

 the microscope, the 

 fibres, which are then 

 clear and pellucid in 

 aspect, appear marked 

 with fine parallel 

 stripes or bands pass- 

 ing across them di- 

 rectly or somewhat 

 obliquely with great 

 regularity (figs, C5 

 and GG, a), and 

 this not only at the 

 surface but, as may 

 be seen by altering 

 the focus of the mi- 

 croscope, throughout 

 its substance also. 

 The stripes are com- 

 monly said to be 

 dark, with light in- 

 tervals ; but it is more 

 correct to speak of 

 both light and dark 

 stripes which alter- 

 nately cross the fibre. 

 The dark and light 

 stripes are nearly of 

 equal breadth, and 

 there also may be seen , 

 very generally but not 

 in all cases, a fine dark dotted line (first noticed by Busk and Huxley) 

 passing along the middle of the light stripe, and dividing it into two 

 (fig. GG, a). About eight or nine dark and as many light stripes may 

 be counted in the length of -^^ of an inch, which would give about 

 T-^i-fT^ inch as the breadth of each. But whilst this may be assigned 

 as their usual breadth, they are in different parts found to be much 

 narrower, so that not unfrequently they are double the above number in 

 an equal space. This closer approximation may generally be noticed in 



w 







if. 



^tr, 



^i'm i 



EJff 



Fig. 66. — A, Portion op x jiedium-sizkd Human Mus- 

 cuLAU Fibre, magnified nearly 800 Diameters, 



B, Separated bundles of Fibrils, equally magnified. 

 a, (I, larger, and b, b, smaller collections ; c, still smaller ; 

 d, d, the smallest wliicli could be detached. 



