2o6 Journal of Comparative Neurology. 



for the larger spindles — compound spindles. The number seems 

 often, however, greater in the immediate vicinity of the larger 

 spindles, due to the fact that now and then, one or the other of 

 the large medullated fibers going to a spindle branches at a very 

 acute angle at some distance from the muscle-spindle. The 

 fibers may approach the muscle-spindle singly, in which case, 

 as is well known, they are surrounded by a thick sheath of 

 Henle, or in small bundles enclosed in a thick connective tissue 

 sheath. The nerve fibers usually enter the spindle from the 

 side, in the smaller spindles, near the center, slightly toward its 

 proximal end, though in the larger compound spindles (see 

 Fig. 39) some of the fibers may enter near the proximal end. 

 In the tortoise now and then, and in the snake more generally, 

 the spindle-nerves enter at the proximal end of the spindle. A 

 portion of Henle's sheath of the spindle-nerves, or of the fibrous- 

 tissue covering of the small bundles of such nerves, becomes 

 continuous with the capsule of the muscle-spindle. Within the 

 capsule, the still medullated nerve fibers, which cross the peri- 

 axial space usually obliquely to reach the axial portion of the 

 spindle, are also surrounded by a connective tissue sheath 

 (Henle's sheath), containing many nuclei, which becomes con- 

 tinuous with the axial sheath, where the nerve fibers penetrate 

 it. The course of the spindle-nerves in the periaxial space 

 varies. They may pass obliquely across the periaxial space to 

 reach the axial sheath, which they may penetrate at once or 

 along which they may run for a short distance before penetra- 

 tion ; they may have a serpentine course in the periaxial space 

 and may be spirally wound around the axial portion of the 

 spindle. The spindle-nerves remain medullated until they have 

 penetrated the axial sheath, within which they may lose the 

 medullary sheath soon after passing through the axial sheath, 

 or may run along a longer or shorter distance between the in- 

 trafusal fibers, having a straight, serpentine, or spiral course, 

 before they lose the sheath of myelin. It has above been inti- 

 mated that the medullated fibers going to the muscle-spindles 

 may branch ; our own observations on this point, as also those 

 on the structure of the spindle nerves, are wholly in accord with 



