212 Journal of Comparative Neurology. 



have several, two, three or four, or perhaps even more such 

 endings ; and these are not always on the same intrafusal fiber, 

 the non-meduUated branches going to this or that intrafusal 

 fiber before ending. 



Birds. Our observations on the muscle-spindles of birds 

 are confined to the dove, and the muscles more particularly 

 studied were several small muscles on the posterior surface of 

 the metatarsus. A i % solution of methylene blue in normal 

 salt was injected into the aorta ; the muscle exposed about one 

 hour after the injection and observed from time to time until 

 the spindle-nerves seemed completely stained. The tissues 

 were fixed in ammonium molybdate, embedded in paraffin, and 

 cut longitudinally and transversely, the sections being further 

 stained in alum cochineal. We may here add that we have 

 found the methylene blue method somewhat unsatisfactory for 

 staining the endings of the spindle-nerves in birds. For some 

 reason which we can not-at present explain, it seems to stain 

 the nerve endings in birds less readily than in the other verte- 

 brates we have examined.' It is usually necessary to expose 

 the previously injected muscle pieces quite a long time to the 

 air, sometimes 30-45 minutes, before the blue color develops in 

 the axis cylinders and their endings ; as a result, the muscle 

 fibers and other structures of the muscle are often stained quite 

 deeply blue, before the nerve fibers are properly stained. In 

 some few instances, however, what we have regarded as a suc- 

 cessful stain of the endings of the spindle-nerves has been ob- 

 tained, and the observations here given are based on such prep- 

 arations. The general structure of the muscle-spindles of birds 

 is as has been previously described. They contain from two to 

 six relatively small intrafusal fibers ; these are surrounded by 

 an axial sheath, periaxial space, and a capsule consisting of 

 three to five concentric layers of fibrous tissue. The intrafusal 

 fibers are further enclosed, each in a separate, thin, fibrous tis- 



1 In some of our later work we now and then found that the nerve fibers 

 were stained a very short time after the removal of the tissue; but also found 

 that such stained fibers bleached very quickly. This may be an explanation as 

 to why we so often failed in staining the spindle-nerves in the bird. 



