The Microscope. 337 



the other and tapering termination not extending to the other 

 tendon but ending within the muscle. I shall call the two terminations 

 respectively, the tendinous and the intramuscular end of the fiber. 

 Figs. 2, 8 and 13 show the relative diameter of these fibers in their 

 different parts, the middle section in each (6), the body of 'the fiber, 

 should be greatly elongated, 40 to 100 times, in order to give an 

 adequate idea of the real form of the fiber. Fibers of this kind 

 were isolated in the latissimus, trapezius, pectoralis, vastus 

 externus, rhomboideus, obliquus abdominis and rectus capitis of the 

 mouse, in the rectus capitis, rhomboideus, vastus externus and two 

 muscles of the brachium of the English sparrow, that is in both 

 limb and trunk muscles. Intramuscular ends were also found where 

 the fibers were not traced their entire length. Most such ends 

 probably belong to tapering fibers. They are found in muscles 

 varying in length from 5 to 27 mm. as the latissimus, trapezius and 

 pectoralis of the English 8parrow,the latissimus, pectoralis,trapezius, 

 vastus externus, obliquus abdominis and one from the back of the 

 bat, and the latissimus, pectoralis and vastus externus of the shrew. 

 In general it may be said that the longer the muscle, the more 

 tapering fibers and intramuscular ends were found. There was no 

 observable difference in number on account of the muscles belong- 

 ing to the trunk or the limbs, nor on account of the species, as in 

 the mouse and bat, nor the age of the animal as in the mouse and 

 sparrow, nor the method of dissociation, whether by nitric acid or 

 caustic potash, provided the specimen was quite fresh. 



3. Fusiform Fibers. — Are those which taper at both" ends (Fig. 

 9). It seems probable that both ends are intramuscular as is so 

 common in the larger animals. In the skeletal muscles only a few 

 fibers of this type were found and these were from the mouse. 

 There were two, each about 10 mm. long from the latissimus, a 

 muscle 25 mm. long, one from the obliquus abdom,inis, one 2 mm. 

 long from the vastus externus, a muscle 16 mm. long, and two 

 others, each 7 mm. long, from the same muscle. The ends in the 

 last named case are clearly intramuscular. In all of these cases the 

 diameter of the fiber is small, that is about one-half the average size. 



4. Length or Tapering Fibers.* — The length of the isolated 

 fibers mentioned under 2, vary in the sparrow from 4 mm. in one 

 muscle (8 mm. long) from the brachium, to 10 mm. in another muscle 

 (18 mm.long) from the brachium; and in the mouse from 6 mm. in the 

 rhomboid (10 mm. long) to 14 mm. in the pectoral (18 mm. long). A 



*The fibers, the length of which is here given, were dissociated in situ (see methods 

 Part II), 80 that only slight allowance need be made for shrinkage. 



