202 Journal of Comparative Neurology. 



correctly states, ' ' its long axis lies parallel to the muscle fibers 

 amid which it is embedded ; " here the distal end of the capsule 

 seems again to become continuous with the internal perimysium. 

 This, it would seem, is the more usual disposition of the distal 

 end of the capsule in amphibia and reptilia, and is now and 

 then found in birds and mammalia. 



In case the muscle-spindle lies near the tendinous insertion 

 of the muscle, in which case the long axis may also be parallel 

 to the muscle fibers amid which it is embedded, or may be at 

 an angle to them, the distal end of the capsule becomes contin- 

 uous with the fibrous tissue septa, or with the tendon ; this we 

 have found to be the more common ending of the spindle-cap- 

 sule in mammalia, but has been seen also in birds and reptilia 

 (tortoise). 



More immediately surrounding the enclosed muscle fibers, 

 designated by Sherrington as ^^ intrafusal fibers,'' there is found 

 a connective tissue sheath which he has described as the ' ' axial 

 sheath,'' consisting of thin bands or plates of white fibrous tis- 

 sue in which nuclei are numerous. 



Between the capsule and the axial sheath is found a rela- 

 tively large lymph space — Golgi and Sherrington — designated 

 by the latter as the ^'periaxial space ; " this, he correctly states, 

 is "bridged across and partially subdivided in many points by 

 extremely tenuous membranes and filaments." The periaxial 

 lymph space is broadest near the middle of the muscle spindle, 

 generally tapering off toward the ends. The intrafusal fibers 

 are sometimes in the middle of this space and again eccentric. 

 The space also shows buddings here and there, which seem, 

 however, in a large measure due to foldings in the capsule, the 

 result of contraction of the contiguous muscle fibers. 



Intrafusal muscle fibers. The intrafusal muscle fibers differ 

 in size and structure from the muscle fibers of striated muscle. 

 Their number varies. In the snake, only one intrafusal fiber is 

 found, as has been stated by Kiihne, Mays, and Sihler ; similar 

 spindles have been found in the lizard by Bremer, Trinchese and 

 Cattaneo. In the other vertebrates examined, the number var- 

 ies from two to ten, and, as Sherrington has stated, in some of 



