The Relation of Muscle Fibrillae to Tendon Fibrillae etc. 257 



adult of the projectioDS of tlie sarcolemma which extend iuto the 

 muscle fibre, They have no connection developmentally or moipho- 

 logically with the tendon fibrillae, since at first there are no tendon 

 fibrillae atfaehed to that portion of the sarcolemma from which 

 these projections are derived. Neither is it probable that they re- 

 present a portion of the muscle fibrillae which might have become 

 transformed into sarcolemma-like tissue. 



This genetic sequeuce explains as well the appearances presented 

 by such muscles as I have represented in the first three figures 

 where the tendon fibrillae and the muscle fibrillae occupy the same 

 linear direction and where in the adult condition the several pointed 

 extremities of the sarcolemma, characteristic of the younger develop- 

 mental stages, are still demonstrable. The tendon fibrillae occupying 

 the intervals between adjaceut extremities assume their position 

 at a stage in the developmental cycle later than the appearance of 

 the definitive form of the muscle fibrillae. In other words, the 

 muscle fibrillae are already attached to the internal surface of the 

 sarcolemma of the intervals before the supplementary tendon fibrillae 

 grow into these intervals and become attached to the external sur- 

 face of the sarcolemma. Accordingly, we can find another argument 

 in this fact of genesis, in addition to the one based upon morpho- 

 logical grounds and mentioned before, against the acceptance of the 

 view that the tendon fibrillae eflfect continuity with the muscle 

 fibrillae by perforating the sarcolemma and then coursiug a con- 

 siderable distauce in the muscle fibre. Indeed, were structural con- 

 tinuity an established fact, if the chronological order of the develop- 

 ment of these »interval« tendon fibrillae and of the muscle fibrillae 

 were alone considered we should expect rather to find a Prolonga- 

 tion of a portion of uudifferentiated muscle fibrillae through and 

 outside of the sarcolemma in order to meet the developing tendon 

 fibrillae, and not vice-versa as some authors have represented. The 

 presence of extrasarcolemmatous muscle fibrillae has never been ob- 

 served among vertebrates, so far as I am aware, and in my own 

 preparations is most positively denied by the staining reactions. 

 The only fibrillae lying outside of the sarcolemma are those which 

 have a conuective tissue origin. 



In general it may be said, then, that the voluntary striped 

 muscles of adult vertebrates terminate in one of two general 

 arrangements the determination of which is dependent upon the 

 relation of the long axis of the tendon to that of the muscle fibre. 



Morpholog. Jahrbuch. 45. 17 



