180 G. E. COGHILL 



stimulation of the cells of the sensory column through the skin. 

 In figures 23 and 25, taken from farther cephalad in the embryos 

 of the early-flexure stage, are shown the relations that such fibers 

 as are illustrated in figure 24 assume with mesenchyme cells 

 beneath the skin. 



(2) The relation of the giant ganglion cells to the myotomes. 

 Figures 1, 3, 4, 7, 10, 14 and 26 have been selected to illustrate 

 the relation which the ganglion cells hold to the muscular system. 



Figure 1 shows this relation in the embryo of the non-motile 

 stage, at the level of the sixth myotome. This fiber projects 

 from a giant ganglion cell through the dorso-lateral border of the 

 cord and applies itself immediately to the caudal end of the myo- 

 . tome. Through the region of this contact it sends spinous proc- 

 esses in between the cells of the myotome. This is essentially 

 the relation seen in figure 15, only from a different point of view. 

 The relation of the fiber with the myotome is just as intimate 

 as is the relation of any of the cutaneous fibers to the skin. The 

 fiber is not simply passing across the surface of the myotome in 

 close contact, but it has clearly differentiated processes that 

 pierce the myotome. Similar relations are shown in figure 3. 

 This contact also is with the end of the myotome. The peripheral 

 fiber is here clearly seen to be a process from the same cell that 

 sends its axone into the sensory tract. 



In figure 4 appears an important bit of evidence on these 

 fibers to the muscular system. Here at the level of the twelfth 

 myotome, a fiber projects latero-dorsad till it emerges from the 

 cord, then, instead of taking a short course through an open 

 field to the skin, it swerves abruptly ventrad to the border of the 

 myotome, upon which it spreads out in a disc-like terminal. It 

 is difficult to conceive of any reason for a skin-sensory fiber to 

 behave in this manner. 



Figures 10 and 11 are taken from successive sections passing 

 between the levels of the fifth and sixth myotomes cephalad of 

 the unsegmented mesoderm in a non-motile embryo. Here the 

 myotomes are closely pressed against the spinal cord, and the 

 nerve fiber emerges from the cord at the dorsal border of the myo- 

 tome. In both the sections the expansion of this fiber upon the 



