126 



TEE CAT. 



[chap. v. 



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

 verse markings, such, sfriation depending on a regular arrangement of 

 alternate parts Avith different refractive properties. Each striation 



Fig. 76.— Striped Muscular Tissue of the Cat, greatly magnified. 



A. Bundle or fasciculus of libres. 

 a. Cut end of a fibre. 



6. A fibre. 



c. A fibre broken up into its component fibrils. 



B. A fibre, witli ])aits of two others. The fibre 



has been split at right angle to its lung a.\is. 



d. One of tlie clefts. 



c. 



Investing membrane or sarcolomma, seen 

 at a jioint of ruiiture. The sarcolemma is 

 twisted, but iU)t brolcen. 

 C. Fibrilla of difl'erent magnitude (/, g, h,) vciy 

 greatly enlarged. 



consists of a central narrow dark line (the septal 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 fibrilla; (Fig. 7C, C), carh fibril .still presenting 

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

 fibre is really made up of naturally distinct fibrilki", since, when 

 treated with much diluted hydrochloric acid each fibre may be broken 

 up into (B d) a number of tliin discs, paraHel to and coinciding with 

 the tran.sverse striations. In the heart, the fibres are branched. 



§ 3. Muscular contraction (^^'hich takes place under certain 



