Huber-DeWitt, Nefve-Endings in Muscles. 213 



sue sheath ; this sheath and the axial sheath contain many nu- 

 clei. Many of the muscle-spindles of birds seen by us have only 

 one area of nerve distribution, but now and then those with 

 two areas have been found. One, two, or three medullated 

 fibers are distributed to each of the smaller spindles or to each 

 area of nerve distribution in the larger — the compound spindles. 

 They are surrounded by a sheath of Henle, which ends, partly 

 in the capsule and partly in the axial sheath. The branching, 

 course, and structure of the spindle-nerves in the bird is as pre- 

 viously described in discussing in a general way the spindle- 

 nerves, and need not here be repeated. They lose their medul- 

 lary sheath within the axial sheath, the non-meduUated contin- 

 uation of the spindle-nerves now and then subdividing into two 

 or three branches. The ending of such non-medullated branch- 

 es is shown in Fig. 3 i ; the fiber a, presenting, we believe, a 

 typical ending. As may here be seen, the axis cylinder (non- 

 medullated terminal branch) ends in an irregular expansion rest- 

 ing on the intrafusal fiber ; from this, processes which resemble 

 somewhat a repeatedly folded ribbon are given off. These pro- 

 cesses show successive broader expansions of round, oval, or 

 irregular shape, united by narrower bridges, and extend for 

 some distance on the intrafusal fiber. In preparations of the 

 whole spindle or in longitudinal sections of a spindle, these pro- 

 cesses are seen on the intrafusal fibers, in optical section by the 

 side of the intrafusal fiber {b of Fig. 31), and also under the 

 fiber. The ending therefore surrounds the intrafusal fiber. 

 Now and then, the non-medullated terminal branches of the 

 spindle-nerves break up at once into two or three processes 

 having the above structure, or, apparently, may continue into 

 such a process ; the latter condition may however be due to im- 

 perfect staining. 



In birds also, a spindle-nerve may have an ending as above 

 described, on more than one intrafusal fiber ; on as many as 

 three fibers ; that these endings are outside of the sarcolemma 

 may be seen in Fig. 32, a cross section of a small muscle-spin- 

 dle of a bird, stained in methylene blue and alum cochineal. 



