134 ALAN C. SUTTON 



these it cannot be said whether the absence of the sensory end- 

 ings is a congenital defect or a late intrauterine degeneration. 

 On the other hand, the congenital absence of single muscles may 

 be due to their failure to receive a sensory nerve. 



Harrison's work on tadpoles has proven conclusively that a 

 nervous connection is not essential for the initial development 

 of the muscle fibers. His experiments, however, do not go far 

 enough to show that the life of a muscle fiber can continue 

 sufficiently without a nervous connection, to give the picture 

 found at birth. It is at this point that I would suggest that 

 the sensory connection is of fundamental importance. It is 

 impossible in view of Harrison's work to agree with Herbst 

 ('01) that the sensory ner\'es are responsible for the initial 

 development. 



In the 65 nun. stage (fig. 7) we see some increase in the size 

 and complexity of the endings. The placques are likewise in- 

 creased in numbers. In all these stages a few of the spindles 

 are farther advanced, others less so, than the ones I have drawn. 

 It is almost impossible to pick out any one and say it is typical 

 for that particular size. However, by taking what I consider 

 the average, stages at 10 to 20 mm. intervals show rather defi- 

 nite progress toward the adult type. In figure 8, taken from a 

 75 mm. embryo, is shown an ending which is equally as numerous 

 in both the 65 mm. and 75 mm. sizes, as the one shown for the 

 65 mm. stage. Here the plexus is spread out a little more but 

 the placques are rather infrequent. 



In figure 9, from a 100 mm. pig, I have represented the nature 

 of the plexus which the axones make among the muscle fibers at 

 this stage with its relation to one of the nerve endings. In every 

 case I have omitted in my sketches, as far as possible, the struc- 

 ture of the surrounding muscle as it would simply complicate 

 the picture without bringing out any important point. This 

 spindle shows the most extensive plexus thus far, with numerous 

 placques. The axones (neurofibrils) after branching upon these 

 placques pass on in most cases to end in delicate tree-like branch- 

 ing along the muscle fiber. 



