On the structure of cross-striated muscle. 231 



accessory disks. The latter therefore since they resist the action of 

 the acid must be distinct structures. This is perfectly true, but may 

 equally well be taken to prove that they are accumulations of sarco- 

 plasm. Rollett, however, in describing the farther action of the acid, 

 goes on to state that these granules also next undergo swelling along 

 with the remaining substance of the muscle-columns, so that the whole 

 fibre now becomes nearly uniformly swollen. The latter statement is 

 also true, for the remainder of the muscle -segments speedily follow 

 the swelling of the sarcous elements. But the dots or granules des- 

 cribed by Rollett as accessory disks, do not in the preparations which 

 I have examined in this manner, share the swelling of the muscle- 

 columns but remain between these, united longitudinally by fine lines 

 of inter-columnar substance, and exhibiting all the characters of the 

 sarcoplasmic enlargements which form the transverse networks. 

 Fig. 24 A shows such an alcohol fibre previous to treatment with acid, 

 Fig. 24 B the same fibre after the action of formic acid. This method 

 then, which is especially mentioned as exhibiting the accessory disks 

 as a constituent of the muscle-column, has in my hands led only to 

 the conclusion that they belong to the inter-columnar substance. 



When we come further to examine into the statements which 

 have been made by various authors relating to the accessory disks, 

 we find that entirely different structures have been described under 

 this term. Some authors, and perhaps the majority, have unquestion- 

 ably had in view the sarcoplasmic dots which represent the trans- 

 verse networks. Others have described the ends of the rod-like 

 sarcous elements, which are often slightly enlarged and rather more 

 •deeply stained than the middle part, as distinct elements of the 

 muscle-segment by this name. And again when, as sometimes happens, 

 there is a double accumulation of sarcoplasm in the position of the 

 transverse networks, the two accumulations giving the appearance of 

 a double row of dots in each clear interval between the sarcous ele- 

 ments and Krause's membrane (and therefore a quadruple row in each 

 clear stripe of the muscle-substance, see Fig. 40), it is clear that 

 since these sarcoplasmic accumulations lie in indentations in the sar- 

 costyles there will be a relative enlargement of the sarcostyle between 



