126 



THE CAT. 



[CHAP. v. 



the appearance of a number of alternating, exceedingly regular, trans- 

 verse markings, such striation depending on a regular arrangement of 

 alternate parts with different refractive properties. Each striation 



Fig. 76. STRIPED MUSCULAR TISSUE OF THE CAT, GREATLY MAGNIFIED. 



A. Bundle or fasciculus of fibres. 

 . Cut end of a fibre. 



fe. A fibre. 



c. A fibre broken up into its component fibrils. 



B. A fibre, with parts of two others. The fibre 



has been split at right angle to its long axis. 



d. One of the clefts. 



e. Investing membrane or sarcolemma, seen 



at a point of rupture. The sarcolemma is 

 twisted, but not broken. 



C. Fibrilla of different magnitude (/, g, Ji,) very 

 greatly enlarged. 



consists of a central narrow dark line (the septdl line], on each side 

 of which is a narrow transparent space (the septal zone), while be- 

 tween the transverse striations is a much larger space (the inter- 

 septal zone), and these larger parts constitute the main substance of 

 the fibre and therefore of the muscle. The appearance thus pre- 

 sented is that of a number of opaque discs embedded, at regular 

 intervals, in a more translucent substance. 



Faint indications of longitudinal division may also be detected, 

 and after immersion in alcohol, or a weak solution of chromic acid, 

 each fibre may be broken up into a number of very much more 

 minute ones termed fibrilla3 (Fig. 76, C), each fibril still presenting 

 the transverse striation. It is, however, by no means sure that each 

 fibre is really made up of naturally distinct fibrillac, since, when 

 treated with much diluted hydrochloric acid each fibre may be broken 

 up into (B d) a number of thin discs, parallel to and coinciding with 

 the transverse striations. In the heart, the fibres are branched. 



3. MUSCULAR CONTRACTION (which takes place under certain 



