156 



LOCOMOTION. 



[CHAP. vii. 



scattered throughout the mass, and some detached 

 ones are represented ; their average diameter is 

 one thousandth of an English inch. 



limit of the cross-stripes; or it may 

 be seen stretching between the se- 

 parated fragments of a fibre which 

 has been broken within it, for its 

 toughness will often resist a force 

 before which its brittle contents 

 give way. If the fibre be im- 

 :UuWii mersed in acid, it swells, often so 



Part of an elementary fibre from the Skate, Suddenly as to burst the sheath 



at numerous P laces > and Protrude 

 in the form of small herniae. 

 These hernise are very peculiar, 

 and illustrate the account already given of the internal composition 

 of the fibre ; for the particles of the protruded mass are necessarily 

 deranged, and their lateral parallelism destroyed. Now, the result 

 of this is the production of the most beautiful and varied curves, 

 intersecting one another, very similar to those already spoken of on 

 the injured fibre, and wearing a very plausible aspect of spirals 

 (fig. 41). Again, the sarcolemma may be seen raised in the form 

 of vesicles from the surface of the fibre, in certain states of con- 

 traction in water, which will be reverted to. By one or more of 

 these modes of demonstration, we know that this isolator of the 

 sarcous tissue invests the striped elementary fibre of voluntary 

 muscle in all animals. Its existence is as yet doubtful in the 

 heart. 



Every fibre is attached by its extremities to fibrous tissue, or to 

 some tissue analogous to it ; but an accurate examination of this 

 difficult subject lends no countenance to the ordinarily received 

 opinion, that this tissue is prolonged over the whole fibre from end 



Fig. 42. 



Elementary fibre from the leg of the large Meat-fly (Musca vomitori<i):a. a. Line of termina- 

 tion of the fibre, along which the tendon, t, is attached to it. m. Central series of corpuscles. 

 Along the margin, the sarcolemma is elevated by water (which has been absorbed), and is thereby 

 shewn to be adherent to the margin of the discs. 



to end, as its cellular sheath ; nor is this view reconcilable with the 

 physical requirements of the case. It is extremely difficult to 



! 



