THE MUSCULAR SYSTEM. 229 



78. The muscular fibres in the trunk and extremities are, in general, 

 so associated, without the existence of any divisions, reticular connec- 

 tion, or termination in the interior of the muscles, as to constitute con- 

 tiguous prismatic bundles extending the entire length of the muscle. 



than the thoracic fibres in the muscles of insects, and the gradual transition of the latter into 

 undoubted bundles, we do not hesitate to regard these thoracic fibres as homologous, not with 

 primitive fibrils, but with primitive bundles; and therefore to neglect any argument which 

 may be drawn from their existence, to that of primitive fibrils during life in the higher 

 animals. 



The answer to the question, whether primitive fibrils exist during life or not, in fact, de- 

 pends very much upon the meaning of the words. If it be meant that the muscular bundle 

 is like a rope, the fibrils being the separate strands, united by " a homogeneous, tenacious 

 substance," we should say that nothing of the kind exists during life. If, on the other 

 hand, it be meant only that the molecules of the muscle are so arranged as to break up more 

 readily and more frequently in the longitudinal direction than any other (just as a bar of 

 wrought iron would tear into longitudinal fibres rather than in any other way, though it 

 could by no means be said that it was composed of longitudinal fibres), why, there can be 

 no question that such is the fact. The behavior of a muscular fasciculus, under the alter- 

 nate action of acetic acid and ammonia, is as instructive with regard to this point, as that of 

 bundles of connective tissue. 



The existence of varicosities of the fibrils must depend very much upon their state of ex- 

 tension. Normally, they do not exist, unless, perhaps, the fibril has been split off from the 

 very edge of a bundle, where the sarcous elements often project strongly. When very much 

 stretched again, since the sarcous elements are more solid and resisting than the matrix, they 

 will form knots, and the fibrils will appear more or less varicose. The great majority of in- 

 stances in which the fibrils appear varicose, however, depend on imperfect definition and 

 the same may be said of supposed zigzag bendings; while the spiral fancies, on the other 

 hand, are more probably connected with an imperfect judgment. 



Recently, Drs. Sharpey (" Quain's Elements") and Carpenter (" Manual of Physiology") 

 have advocated a view, the former, however, with some doubts (to which Professor Kolliker 

 does not refer), founded upon an examination of the preparations of muscular fibrils, made 

 by Mr. Lealand. They distinguish quadrilateral dark spaces in the fibrillae, each of which 

 is set, as it were, in a transparent frame of the same shape; these joined together constitute 

 the fibril, the lines of junction of the frames, or "cells" being indicated by a dark line. We 

 have repeatedly seen the appearances which are thus described; but so far as we have 

 been able to discover, they invariably arise from that peculiar interposition of rows of mi- 

 nute paler sarcous elements, between the ordinary broad dark ones, to which we have re- 

 ferred above in describing the muscles of insects. 



Very often, the finer sarcous elements are completely wanting, as in the thoracic muscles 

 of Insects, in the muscles of the Frog, and in many of the bundles in Mammals; and in 

 these cases there is, of course, no evidence at all of the existence of any such "cells." 



In conclusion, we may state the view which we are led to take of the structure of striped 

 muscle, in a few words. In a homogeneous, transparent matrix, definite particles are im- 

 bedded the sarcous elements, which are arranged side by side, in even transverse rows. 

 In some cases the sarcous elements are all of one size; in others, they are alternately larger 

 and smaller. The reason of this difference does not at present appear, but'it is very pos- 

 sibly connected with the nutrition of the muscle. The matrix usually tends to break up 

 into longitudinal bands the " fibrils," which have the diameter either of a single sarcous 

 element, or of some multiple thereof; it likewise tends to break up in the transverse direc- 

 tion, giving way between the pairs of rows (discs) of sarcous elements ; but these cleavage 

 lines are no indication of the existence of discs or fibrils, as such in the unaltered muscle. 

 The sarcolernma is simply the outer portion of the matrix, and its demonstrability as a sepa- 

 rate structure depends upon the extent to which it is developed, and the amount of chemical 

 change which it may have undergone relatively to the inner portion. TBS.] 



