The Relation of Muscle Fibrillae to Tendon Fibrillae etc. 251 



able up to the internal surface of the sarcolemma. There is no 

 evidence, however, either upon morphological or upon staining- 

 reaction grounds for the assumption that the fibrillae of muscle and 

 tendon penetrate the sarcolemma. Neither can it be demonstrated 

 that the sarcolemma is prolonged over the tendon or among- its con- 

 stituent fibril bundles. It terminates bluntly, rather, in a number 

 of cone-shaped processes. 



Fig. 3 represents the termination of an extrinsic muscle of the 

 eyeball of a twenty-two-day-old white mouse. The observations 

 made above in connection with the chicken muscles apply equally 

 well to the muscles of this group in the mouse. Again, there is 

 observcd, the dovetailing of the sarcolemma processes with the 

 tendon fibrillae, the termination of the muscle fibrillae at the sarco- 

 lemma, and the Separation by the latter of the tendon fibrillae from 

 the former. 



I particularly desire to refer again to the Insertion of the tendon 

 fibrillae into the intervals betvveen the cone-shaped prolongations 

 of the sarcolemma through which arrangement certain appearances 

 are produced which are exceediugly liable to be misinterpreted. This 

 thin membrane is the only structure separating the muscle fibrillae 

 from the tendon fibrillae. The latter pursue a course parallel to 

 that of the former but terminate bluntly upon the external surface 

 of the sarcolemma, whereas the muscle fibrillae run for a com- 

 paratively short distance upon the internal surface of the sarco- 

 lemma and finally lose their identity by fusing with it. Such con- 

 clusions can only be drawn from a study of those fibrillae which 

 lie upon the same horizontal optical plane, i. e., upon that aspect of 

 the sarcolemma which faces at right angle to tbe observer. When 

 the muscle fibres and tendon fibres are cut in exactly their long 

 axis, one must bear in mind that the uppermost and undermost 

 aspects of the cone-shaped sarcolemma end are obliquely inclined 

 to the vertical optical axis of the observer. This fact adds to the 

 difficulty of interpreting the relation of the fibrillae more so than 

 would be the case if the sarcolemma surface lay in a horizontal 

 optical plane. Hence the Solution of the question is much dependent 

 upon the manipulation of the fine adjustment screw. Bearing in 

 mind the fact that the sarcolemma is so thin as to be almost per- 

 fectly transparent, when studied upon these aspects of the fibres, 

 the difficulty in determining the exact relationship of the muscle 

 fibrillae to the overlying or underlying and parallel-running tendon 



