THE NEURO-MUSCULAR SPINDLE 119 



In a later article ('02) he says: 



The final union of the growing tip of the nerve with muscle cells 

 seem in the rectus muscle of the pig to begin in embryos of 8 cm. but 

 definite endings are few until considerably later. The formation of 

 nerve-endings cannot be satisfactorily followed in mammalian em- 

 bryos, owing to the great number and small size of the cells 



Union of nerve fiber and muscle cells does not begin to be common 

 until this embryo has reached a length of 15 cm. and it continues for a 



considerable time after this period The development of 



the sensory and vaso -motor apparatus can only be followed with satis- 

 faction when better methods for differentially staining developing 

 nerves have been devised. Methylene blue, which is so good for adult 

 tissues seems to act much less specifically on developing nerve fibers. 



Bardeen's work was done with gold chloride preparations. 

 Kolliker ('05) in contradiction to the much earlier doctrine of 

 Schultze ('85) that the endings arise from 'cell nets' advanced 

 the now generally accepted view that both sensory and motor 

 ending can each be traced back to a single cell. Schultze had 

 been misled by the nuclei of the sheath cells of Schwann which 

 grow out along the axones — prior to medullation — and beyond it 

 on to the naked fibers of the endings. Felix ('89) has made an 

 extended study of the muscle spindle as a whole, in the human 

 embryo, under the mistaken idea that they represented specific 

 areas for the production of new muscle cells after such production 

 by multiplication of myoblasts had ceased. He did not, however, 

 work out the relation of the nerve to muscle. London and 

 Pesker ('06) give four Unes to their own work on the subject: 

 ' ' The development of the spiral sensory endings is in this way — 

 the end fibers branch profusely and surround spirally the muscle 

 fibers which are likewise increasing in size." In their article 

 they give two figures of sensory endings, ten figures of nerve 

 outgrowths and one figure of motor endings. They call them all 

 muscle spindles. Twelve of them are taken from mouse em- 

 bryos 1.2-1.6 cm. long, one from a mouse two weeks old. The 

 drawings are rather unsatisfactory. The paper is chiefly a 

 discussion of literature upon various points of controversy. 



It was largelj^ on account of the wealth of material that was 

 at hand, together with the fact that I had previously done some 



