MUSCLE STRUCTURE 



41 



scope, the fasciculi are seen to be bundles of fibres 

 packed tightly together. These fibres, when traced 

 throughout their length, are found to be slender hair- 

 like cells about one and a half inches long and one- 

 thousandth of an inch in diameter, crossed by many 

 dark and light bands and covered with a thin mem- 

 brane. Each fibre in turn consists of many much finer 

 contractile threads, the fibrils. 



Tendon fibres. To one or both ends of each of the 

 muscle fibres is usually attached a fine silky thread of 



'Contractile 

 fibrillae 



-Striae 



Nucleus 

 of sheath 



Cement 

 Substance 

 Tendon 

 fibre 



PIG. 32. End of striated (voluntary) 

 muscle fibre, showing its attach- 

 ment to tendon fibre. 



FIG. 33. Diagram showing arrange- 

 ment of muscle fibres in relation to 

 their tendons : A, in muscles con- 

 tracting through a considerable dis- 

 tance ; B, in muscles of shorter and 

 more powerful contraction ; C, in 

 muscles of very short and powerful 

 contraction. 



tough inelastic material, the tendon fibre. Since the 

 muscle fibres are usually much shorter than the muscle 

 itself, these threads have to run well up into the muscle 

 in order to reach the ends of the fibres. By blending 

 together, they form the strong hard continuation of the 

 muscle, the tendon, which joins the muscle to the bone. 



