228 The Microscope. 



frequent length of tapering fibers in both animals is 6 to 9 mm. and 

 generally speaking, they are from one-half to two-thirds the length 

 of the muscle in which they occur, but occasionally, as in the rhom- 

 boid, which is 9 mm. long, and the rectus capitis, which is 5 mm. 

 long, they extend from one tendon nearly to the other. 



Owing to the difiiculty of preparation, perfectly isolated taper- 

 ing fibers are comparatively few, hence it seems desirable to confirm 

 the above statement by other facts, (a.) Intramuscular ends of 

 fibers which were not traced to the other end, are generally found 

 near the middle and in the middle third of the muscle and only 

 occasionally near the tendon. Of the last, some perhaps may belong 

 to fusiform fibers (see 3). (&.) In dissecting thoroughly disso- 

 ciated muscles by needles, an apparent rupture sometimes occurred 

 at about the middle of the muscle. This proved, upon examination, 

 not to be a tear, but on each side of the break were found groups of 

 tapering intramuscular ends which evidently had interdigitated, and 

 which belong to fibers, somewhat over half the length of the muscle, 

 coming from opposite tendons. (c.) The examination of serial 

 transections of the vastus externus of the mouse shows that while 

 occasionally not far from a tendon is a fiber of very small diameter, 

 that is the tapering end of fiber, the majority of such ends is near 

 the middle of the muscle (Figs. 19-21). 



From all these facts it seems justifiable to say that tapering 

 fibers in these animals are generally from one-half to two-thirds of 

 the length of the muscle in which they occur, that is from 3 to 18 

 or 20 mm. long, with an occasional one which is nearly as long as 

 the muscle itself. 



5. Diameter or Fibers. — Fibers from the mouse show in transec- 

 tion a great variety of form, being circular, triangular, quadrilateral, 

 etc. (Fig. 19-22). Isolated fibers from all the small animals 

 examined gave evidence of a similar variety in form, some of them 

 when twisted show that they are even ribbon- shaped. The intra- 

 muscular ends approach more nearly to the cylindrical form than the 

 fibers at their full size, as seen in section (compare Fig. 20 and 22), 

 but even here they are often irregular (Fig. 21). In isolated pre- 

 parations the simple tapering form of intramuscular end (Fig. 2-4) 

 gives the appearance of a more regular cylindrical form than a 

 branched ending does, as shown when an end rolls over or is twisted, 

 while the tendinous ends frequently appear thin and much expanded 

 laterally (Fig. 6), or compressed and tapering (Fig. 5). From 

 these facts it is seen that though the type of the fiber is either cyl- 



