Wilson, Motor Endings of the Frog. 1 1 



or compressed. As the fibrils subdivided each branch was sur- 

 rounded by a sheath which became fainter as the nerve fibril 

 became finer. 



Occasionally there coiled round a primary terminal branch 

 of a nerve ending another nerve in no way related either to 

 this nerve ending or to its muscle fiber. Thus in Fig. 5 at (2) 

 the nerve (3) curved round a primary terminal division of 

 the nerve termination on muscle fiber A. This is only 

 to be explained by one of two suppositions ; either both 

 nerves at that point were over the sarcolemma or under it. The 

 latter supposition is open to many objections ; the former will 

 generally be acknowledged to be the more probable, and to me 

 is a confirmation of what I have already stated. 



Attention was now directed to two points : 



(i) The relation of terminal fibrillae and of the end knobs 

 to the sarcolemma ; 



(2) The relation of the ultraterminal fibrillae to a sheath. 



In sections where very fine fibrils were seen, one could 

 trace the blending of the nerve sheath with the sarcolemma. 

 In Fig. 9 the terminal nerve fibrilla rested on an apparently 

 homogeneous substance which was not separated from the con- 

 tractile muscle substance by any sarcolemma and which was 

 covered by a cap formed by the blending of the nerve sheath 

 with the sarcolemma. In short, it lay under the sarcolemma. 

 When the section from which Fig. 9 was drawn, was carefully 

 examined under the 1.5 mm. Zeiss apochromatic and Oc. 6, 

 the sarcolemma appeared at {a) to split into very faint lines. 

 Two of these were seen to project as at (<a!) and disappear in 

 the covering cap. Similarly at [b) a line was seen to go off as 

 delineated. The impression formed by the study of this and of 

 other similar sections, was that though the cap over the termi- 

 nal nerve fibrilla or end-knob was formed by the blending of 

 the sheath which surrounded the nerve fibril with the sarco- 

 lemma, the tissue which had principally to do with its formation 

 was the sheath of the nerve fibril. 



The relation of the root-like knob to the muscle fiber was 

 sometimes particularly interesting. It seems to lie more in the 



