THE NEURO-MUSCULAR SPINDLE 139 



stretch over to the next placque, where we get a similar appearance. 

 There is a great similarity between these and the true muscle spindles. 

 The two may at times be continuous. 



I am strongly impressed that the early placque which I 

 have described is the basis upon which the nem-ofibrillar net is 

 stimulated to form and in the later stages is obscured by it. I 

 am sure that it differs in composition from both the muscle and 

 nerve and that it is not a very fine neurofibril net. It stains 

 rather characteristically and is constant in nature. It looks 

 coarsely granular under high magnifications. By teasing out 

 one of the muscle fibers from a spindle one will find at times that 

 a placque will separate from the sarcolemma (fig. 12). If the 

 fiber is now crushed in glycerine between a cover-slip and slide, 

 other placques can be removed in a similar way, with the nerve 

 plexus still intact upon them. This would show that they are 

 distinct from the muscle fiber. In a number of instances I was 

 then able to crush these placques further so that they separated 

 sharply from the rather wiry little nerve filament (fig. 12). If it 

 had simply been a delicate plexus of the nerve filament, the 

 latter, after being torn loose, should have shown a few torn 

 branches, but instead it was perfectly smooth throughout. 

 Then too, when the placque did go to pieces its consistency did 

 not impress one as that of a delicate network of fibers. I am 

 rather inclined to look upon it as an intermediate substance 

 between the neurofibrils and myofibrils. 



That an intermediate substance does occur in the motor 

 endings, most neurologists are agreed; this is based upon the 

 action of curare, the South American arrow poison. We also 

 know from Langley's work that this substance does not partici- 

 pate in the degeneration of the motor nerves. Langley holds the 

 view that the receptive substances are radicles of the contractile 

 molecule, and that those at the nerve ending are special develop- 

 ments of those present throughout the muscle fiber. As yet there 

 is no anatomical basis for this substance. Boecke in his work 

 upon the development of the motor endings reaches the conclu- 

 sion that the neurofibrils and myofibrils are continuous in the 

 motor plate. However, I think here the physiological evidence 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 18, NO. 1 



