SYMPATHETIC GANGLIA 241 



tions of embryos 6 mm. in length, the anlage of this ganghon ap- 

 pears as a group of cells pushing out ventro-mesially from the 

 periphery of the Gasserian ganglion along the wall of a large 

 blood vessel lying in close proximity with the latter (fig. Q, sy 2). 



The anlage of this sympathetic ganglion remains broadly con- 

 nected with the Gasserian ganglion for some time. As develop- 

 ment advances, the cells in this ganglion become more closely 

 aggregated and the cellular tract by which it is connected with 

 the Gasserian ganglion becomes relatively narrow. In em- 

 bryos 10 nam. in length, the second sympathetic ganglion is al- 

 most completely separated from the Gasserian ganglion but re- 

 mains in close proximity with it (fig. 7, sy 2). This ganglion, 

 doubtless, arises more or less directly from the Gasserian ganglion. 

 The second and third sympathetic ganglia, however, are not en- 

 tirely distinct during embryonic development. As early as the 

 sympathetic trunk may be traced at this level, numerous sympa- 

 thetic cells are present among its fibers between these two gan- 

 glia. It is not impossible, therefore, that the second sympathetic 

 ganglion may be genetically related to both the V and VII cranial 

 nerves. The great majority of its cells, however, are, doubtless, 

 derived directly from the Gasserian ganglion. 



Cephalad of the second sympathetic ganglion, the sympathetic 

 trunk soon enters the first sjTiipathetic ganglion which is inti*- 

 mately associated with the anterior portion of the Gasserian 

 ganglion. In transverse sections of embryos 6 to 10 mm. in 

 length taken through the anterior region of the Gasserian gan- 

 glion, the anlage of the first sympathetic ganglion may be ob- 

 served on the ventro-mesial surface of the Gasserian ganglion. 

 During the early stages of development, the sympathetic por- 

 tion of the ganglionic mass can hardly be distinguished. In the 

 earliest stages, the cells destined to become differentiated into 

 sjrmpathetic ganglion cells are identical in appearance with the 

 cells of the cerebro-spinal ganglia. As development advances, 

 the cells of the cerebro-spinal ganglia increase in size more rapidly 

 than do the sjnipathetic cells. The sympathetic anlage associated 

 with the Gasserian ganglion may, therefore, be recognized by the 



