366 



MUSCULAR MOTION. 



delicate tubular sheath or sarcolemma, which may be distinctly 



when the two ends of a fibre are 



Fig. 148. 



seen, 



twi 

 Bowman.) 



Fig. 149. 



drawn apart. The contained fibrillse 

 will rupture, whilst the sheath remains 

 entire, as represented in Fig. 148. 

 During the act of contraction, it is also 

 sometimes observed to rise up in wrin- 

 kles, upon the surface of the fibre, as in 

 Fig. 166. It is distinct from the cellu- 



Fragments of an Elementary Fibre of lar tissue that binds the fibres into fas- 



the Skate, held together by the untora c [ cu \i* (] oes no t appear to be perforated 



but twisted Sarcolemma. (Todd & .\ r , 



by nerves or capillary vessels; ana evi- 

 , dently has no share in 



the contraction of the 

 fibre. Although com- 

 monly described as cy- 

 lindrical, these fibres 

 would seem to be rather 

 of a polygonal form, 

 their sides being flat- 

 tened against those of 

 the adjoining fibres. 

 Their size varies greatly 

 in different classes of 

 animals, and even in 

 the same animal, and 

 the same mus,cle. Mr. 

 Bowman found them to 

 be, in the human male, 

 from 5 J 7 to T J 3 of an 

 inch; in the female, 

 from g -Jg to ^ J ? , and it 

 has been estimated, that each fibre may be 

 composed of from 500 to 800 fibrillse. Il- 

 lustration, Fig. 149, representing a trans- 

 verse section of the fibres from the pectoral 

 muscle of a teal; and Fig. 150, a transverse 

 section of the ultimate fibres of the biceps, 

 exhibit well the irregular shape and size, 

 and the cut extremities of fibrils that go to 

 the constitution of the fibre. Under the 

 microscope each fibre exhibits a close alter- 

 nation of light and dark lines crossing it 

 transversely, which are presumed to be 

 owing to the arrangement of beaded fibrillae, 

 as shown in Fig. 151. The beaded enlargements of the fibrillse seem 

 to adhere closely to each other, so that when the extremities of a fibre 

 are drawn apart, it not unfrequently happens, that the disks formed by 

 them separate. 



It has keen affirmed, that the primitive component segments of the 



Transverse Section of Fibres from the Pectoral Muscle of a 

 Teal. 



Fig. 150. 



Transverse Section of Ultimate Fi- 

 bres of Biceps. (Bowman.) 



