THE NERVOUS SYSTEM OF AMPHIBIA 181 



myotome and its projections in between the myotome cells are 

 clearly shown. In figure 11 the relation of the terminal as it 

 applies itself closely over a yolk spherule, partially encircling it, 

 is typical of these endings. In this figure also the process from 

 the same cell can be seen ascending into the sensory tract. 



Figures 7, 12 and 13, taken from an embryo of the non-motile 

 stage, illustrate the terminations of these fibers upon the muscles 

 by smaller branches. In figure 7 there is a terminal upon one 

 myotome and branches out towards the other; in figure 13, there 

 are terminals upon both myotomes. Figure 12 is introduced 

 because it represents one of the clearest cases of the relation of 

 these finer branches of the nerve fibers to the myotomes. Within 

 the cord, it should be noted, the process of the cell projects towards 

 the myotome directly. Immediately after emerging through the 

 external limiting membrane it divides into a more dorsal and a 

 more ventral division. The destination of the dorsal division is not 

 certain, although it apparently sends filaments into the myotome. 

 The ventral division, however, sends a process directly against 

 the myotome, where it spreads in both directions and pierces the 

 myotome by fine, spinous processes. There can be no doubt 

 about the origin and nature of this fiber and the only reasonable 

 interpretation is that it, in part, terminates in the myotome as 

 indicated in the figure. 



Figure 14 is taken from the level between the second and third 

 myotomes cephalad of the unsegmented mesoderm, in an embryo 

 of the non-motile stage. It shows how the myotome at this level 

 is closely pressed against the spinal cord so that a mere line marks 

 the boundary between the structures. i\.t the dorsal border of 

 this contact a giant ganglion cell fiber emerges from the cord 

 against the myotome at its end. As it passes across the end of 

 the cells it sends the characteristic spinous processes into the 

 myotome. Farther out it spreads out into an amoeboid film, 

 which is applied to the myotome at one edge and extends out 

 towards the skin at the other. 



In figure 26 is shown the only case which has been observed 

 where, by chance, the nerve fiber to the myotome has been dis- 

 connected, in part, from the myotome so as to show clearly the 



