7S4 



A. SUIJHA llAU AND V. U. JOHNSON ON TJlli NEUVOUS 



E. The Secondary Sym2^athetic N'erve Cords. 



An interestiug example of this union is sliown in text.-fig. 9 F, 

 a leconstniction of Sparrow 60 (= about G-doy cliick). We here 

 see that at two points the secondary chain is actually completed, 

 while in other places marked caudal prolongations are apparent. 

 The completion of the formation of these definitive sympathetic 

 chains is found at a stage corresponding to that of the seven-day 



Text-figure 10 (a & h). 



Diftgvamniatic figures sliowing relations of sympathetic cord to sun-ouiuliiig tissues 

 as si'ou in transverse sections of Sparrow 13 at points marked a-a, u-jj in 

 fis. 9 D. ' 

 lOrt. Pusses through a ganglionic swelling of the sympathetic chain (Si/m.C). 

 The ganglionic swelling lies dorso-lateral to the aorta {1).A.) and between 

 the segmental artery (Set/. A.) and segmental vein (Sei). 1'',). There is a dorso- 

 lateral projection pointing towards the position of the dorsal root ganglion. 



10 i. Passes through a connective (P. S.C.) between two ganglionic swellings. 

 The, two sections are only 56 p apart. 



J). A. Dorsal aorta. D.R.O. Dorsal root ganglion. M^t. Myotome. 

 Ntc. Notochord. Sp N. Spinal nerve. 



chick. A reconstruction of this stage is shown in text-fig. 9 G, 



SpiUTOW B. 



The condition of the primary sympathetic chain at this stage 

 presents very interesting features. The two cords are now much 

 diminislied in size and, gradually approaching one anothei-, are 

 for some distance almost in contact. Their moniliform character 

 is lost, except that in the thoracic' region wo find three large 



