118 ALAN C. SUTTON 



Langley — which is acted upon by curare, and which does not 

 degenerate with the nerve when the latter is cut? Although 

 there may not be complete evidence to warrant an affirmative 

 answer to this question, one of the findings of my work upon the 

 development of the muscle spindle makes it essential to consider 

 such a structure as a possibility, if not a probability. I will 

 take this question up more fully later, when I come to the actual 

 description of the neuro-muscular spindles in the embryonic 

 muscle. Following the demonstration of the unique spindle in 

 the muscle with its apparently highly specialized structure, nat- 

 urally the next question to be settled was, what function has it? 

 This was admirably answered by Ruffini and Sherrington, the 

 former reasoning out its necessary action from its histological 

 structure ; the latter confirming his conclusions by that now well- 

 known experiment of cutting the ventral roots of the nerves to 

 one of the limbs of -a cat and finding that the intrafusal nerve 

 fibers did not participate in the Wallerian degeneration which 

 affected all the motor nerves of the limb muscles. Prior to Sher- 

 rington's work any ideas as to the function had been largely a 

 matter of conjecture. Still, Charles Bell, as early as 1826, had 

 believed in the entity of a distinct muscle sense — the so-called 

 ''sixth sense of Bell" — for which he believed an anatomical basis 

 would some day be found. The final phase of the work — the 

 embryological development of the muscle spindle — seemed to me 

 neglected, perhaps because it had not impressed anyone as being 

 very important, or more likely, because the material was not 

 conveniently to be had for this study. 



The few statements bearing upon the sensory nerve endings 

 in embryos that I have been able to find in the literature are in 

 articles by Bardeen, Kolliker, Schultze, Felix, and indirectly by 

 London and Pesker. Bardeen ('00) says: 



It is only comparatively late in embryonic development that ter- 

 minal nerve fibers or fibrils enter into intimate relation with tissue 

 elements. I have succeeded in staining them with methylene blue and 

 gold chloride and the earliest unions I have seen have been in 6-7 

 centimeter pig embryos. I believe, however, the union of the nerve 

 fibers and muscle cells occurs considerably earlier. 



