156 Journal of Comparative Neurology. 



ment, he has reference also to the axis cylinders : ' ' The nerve- 

 fibers in so terminating frequently become thick .... with 

 shortened internodes." The bundles of small medullated fibers, 

 as also the single fibers, are surrounded by a distinct fibrous 

 sheath — a sheath of Henle. 



The end-organs in question (which, as may here be stated, 

 are simple neurotendinous spindles) consist of a tendon fasci- 

 culus surrounded by a thin, closely fitting fibrous sheath in which 

 oval or oblong nuclei are found. (The sheaths surrounding the 

 tendon fasciculi are not shown in the figure ; they are not 

 clearly seen in preparations mounted in ammonium-picrate-gly- 

 cerine ; they are, however, readily made out in sections of tis- 

 sue fixed in ammonium molybdate.) This sheath becomes in- 

 distinct at the central and peripheral end of the end-organs and 

 seems to blend with the fibrous tissue found between the ten- 

 don fasciculi and muscle fibers. The shape of this end-organ is 

 more that of a cylinder than a spindle, as neither the tendon 

 facsciulus nor the space between it and the sheath, which in all 

 parts is narrow, are perceptibly thickened in the equatorial re- 

 gion. As above stated, one or two medullated fibers terminate 

 in each end-organ. They pass through the fibrous sheath as 

 medullated fibers with short internodes, losing the medullary 

 sheath soon ^ifter entering. The naked axis cylinders then 

 break up into several divergent branches, which undergo re- 

 peated further division, the resultant branches bearing the char- 

 acter of non-medullated fibers with numerous irregular varicos- 

 ities of variable size. These terminal branches become so inter- 

 laced and interwoven that in a well stained preparation it be- 

 comes very difficult to follow them. I have attempted to 

 reproduce these endings in the accompanying figure, to which 

 the reader is referred in lieu of a more detailed description. 

 This plexus is spread out over the tendon fasciculus, but under 

 the fibrous sheath surrounding it. Some of the terminal 

 branches penetrate the tendon fasciculus for a short distance, as 

 may be seen in cross-sections. 



The nerve termination here described differs in many re- 

 spects from that found in the neuro-tendinous spindles found in 



