120 Journal of Couiparative Neurology and Psychology. 



thetic occurring as an almost unbroken rod of cells (Fig's. 2 and 

 8. Sy.). 



Behind the second nerve, the sympathetic ridge is much 

 Vviffber and much better defined than in the preceding stage ; 



/^«^. 2. — Transverse section through a 12.5 mm. toad, midway between the 

 first and second spinal nerve (see Fig. 8), showing cells becoming aggregated to 

 form the sympathetic cord, {Sy.). Ao. 2., aorta (of one side, where double). Ch., 

 notochord. In., intestine. Sp. Ca., spinal canal. X 246. Camera lucida. 

 Reichart, oc. 2, obj. 7 a. 



the outer cells of it are becoming more closely compacted and, 

 in some places, a definitely limiting membrane has been differ- 

 entiated. This group of cells is the beginning of the diffcrcntia- 

 iio?i of the sympathetic cord in the body region. In some places, 

 this cord includes a part or all of the ridge, this being especial- 

 ly noticeable anteriorly, just in front of the point where the me- 

 dian dorsal aorta begins (Fig. 8, *). Fig. 3 is taken in this re- 

 gion, and shows nearly the whole of the ridge being formed into 

 the sympathetic cord iSy.). 



The cellular structure with which the sympathetic ridge is 

 connected, remains the same as in the preceding stage, except 

 for a general increase in size and an enlargement, in the region 

 of the fourth nerve (cf. Fig's. 7 and 8, Ma.). This enlarge- 



