1881.] the Striation of Voluntary Muscular Tissue. 2>11 



So far we are led to consider the fibre as made up of many ampul- 

 lated fibrils, packed side by side, forming an ampullated fibre, these 

 fibrils being uniform throughout, and joined together by some cement- 

 ing material, the nature of which we will not surmise. The only point 

 which would suggest a definite structure along the fibril is the attach- 

 ment of the sarcolemma in insects' muscle to Dobie's lines. There is 

 no doubt that this membrane dips down and seems prolonged into 

 Dobie's lines in a most beautiful and regular manner. The signifi- 

 cance of this is very obscure, and is quite beyond me. There are 

 many possibilities. It may be, although there is no proof of it, that a 

 membrane exists here continuous with the sarcolemma ; it may be 

 that there is nothing but some cementing substance more soluble in 

 alcohol than the sarcous matter : it may be that there is a little minor 

 crest at this point to which the sarcolemma is attached. This little 

 crest I have certainly seen in some fibres, and it has already been 

 figured by more than one writer, yet in other fibres, the outlines of which 

 are wonderfully distinct, no trace of it is to be made out. The fibres 

 can hardly be said to break across in the line of Dobie, all that can 

 definitely be affirmed is that they cleave in the thinnest part, or the 

 light stripe. The investigation of this point is one of great difficulty, 

 owing to the haze around the broken points, and I can never make up 

 my mind to any definite statement. This transverse cleavage is not 

 of course a point of very much weight, as the fibre would naturally 

 tend to split across in or near Dobie's lines, as here it is thinnest. 



The striping of muscle can be easily explained, as shown before, 

 which leads me to my final statement. A fibril is structureless through- 

 out its entire length, except that, perhaps, there may be membranes, 

 or lines of fission, or layers of cement at the positions of the Hues of 

 Dobie ; this we leave an open question. In using the word " struc- 

 tureless," I must not be misunderstood ; structureless membranes and 

 tissues are fast losing their place in histology, and once simple proto- 

 plasm is now most complex. What I infer is that the stripes do not 

 mark the positions of alternating layers of different structure, the 

 presence of which are ordinarily maintained. The complicated 

 " Muskelkastchen " of the Germans do not exist. 



The muscular tissue of the heart presents many peculiarities which 

 it is needless here to enumerate, for the cross striping alone concerns us. 

 All those cross bands which have been described in oidinary voluntary 

 muscle may here also be seen, and they are placed in the same rela- 

 tions with the turned surface of the fibre. The dark stripe correspond- 

 ing to the crests, or ridges, the light bands to the depressions between 

 them. (Fig. 7.) Dobie's lines may be made out with great ease, and 

 as there is no sarcolemma here, they may be accounted for also purely 

 from the shape of the fibres. I have often thought that Dobie's 

 lines marked the positions of tiny ridges in the valleys, but this is a 



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