Jones, Development of the SympatJietic. 



121 



ment persists in later stages, being distinctly noticeable in i8 

 mm. embryos, and is due to relationship with another structure, 

 this relation suggesting that between the sympathetic and the 

 adrenals described by Minot.^ The relation of the spinal 

 nerves to the developing sympathetic system is practically the 

 same as in the 9 mm. stage, except in the case of the sixth, 

 where the cord is somewhat removed from the nerve, retaining 

 distinctly, however, short fibrous connections. These fibers 

 constitute the beginning of a ramus communicans (Fig. 8, 7?.). 



Fig. J. — Transverse section of a 12.5 mm. toad, between the third and fourth 

 spinal nerves (see Fig. 8), showing nearly the whole of the sympathetic ridge be- 

 ing transformed into the sympathetic cord, Sy. Pg., pigment. Cf. neck of cells 

 marked t with Fig. 5, Rt. Other abbreviations, same as in ffig's. i and 2. X 

 246. Camera lucida. Reichert, oc. 2, obj. 7 a. 



Fourteen Millimeter Stage. — At this stage, the sympathetic 

 cord is easily traced between the second spinal nerve and the 

 vagus ganglion, except immediately behind the first nerve (Fig. 

 9, Sy.y., connection with the vagus ganglion is uncertain. 



Posterior to the second nerve, the ridge now has become 

 much more prominent. In many places, it becomes high and 

 narrow (Fig's. 6 and 10, Ri.) before the sympathetic cord is dif- 

 ferentiated at the free border of it (Fig's. 5 and 6, Ri. and Sy.^. 



'"Human Embryology." Pages 485-489. 



