SYSTEM AND SUIMIAIIENAL BODIES IN THE SPARROW. 753 



cells in both ganglia and processes. The posterior part of tlie 

 chain in text-fig. 9C still shows considerable dispersion of the 

 sympathetic elements, and it is from this region that contril)u- 

 tions are sent to the suprarenal bodies. In the anterior part Ihe 

 chains are united by transverse commissures. 



Text-Hg. 9 1) represents a reconstruction of Sparrow 13 

 (= 96-hr. chick). The distinction between ganglia nnd con- 

 nectives is much more marked, nnd an important change is also 

 visible in the lateral processes. The four anterior paii-s are still 

 united by a broad base to the primary ganglia, but instead of 

 tapering to a point thoy are now of practically the same thick- 

 ness throughout. In the three posterior pairs the bases show 

 signs of constriction, while the distal portion is marked by a 

 cranio-caudal elongation. Now when we examine the cords 

 themselves we find that they are thinnest just in the region 

 where the lateral processes possess these cranio-caudal exten- 

 sions, while in the anterior region, where the processes have 

 not yet reached this stage, the cords remain of considerable 

 thickness. We are again driven to the conclusion that the 

 cranio-caudal extensions are formed at the expense of the 

 primary cords. 



Text-fig. 9 E, from Sparrow A (= 5^-day chick), shows a con- 

 tinuation of this development. The lateral processes are now 

 solid masses, united to the primary chain by short connectives, 

 and all of them show cranio-caudal extensions, the caudal being 

 more mai'ked. The correlation between the increased size of the 

 lateral process and the thinness of the primary sympathetic chain 

 is again very obvious. 



The solid lateral masses are now situated in close relationship 

 with the spinal nerves, being located just mesial to the junction 

 of dorsal and ventral nerve roots. They may now be termed the 

 primordia of the secondary sympathetic ganglia. Subsequent 

 growth of their cranio-caudal extensions leads by their uiiion to 

 the formation of the definitive sympathetic chain (secondary 

 sympathetic chain). 



J). Ikconstntctioii of SiiaiTow 13 (=OG-lir. chick). Gnnglia Jiiid coniuc- 

 tives iiioro mnvked. Lateral i)rocosses tliickenod. Posterior ones con- 

 stricted to some extent. 



K. lleconstriictiou of Sparrow A (Si-dny cliick). f.atcral processes now 

 solid masses united to the primary chain by short connectives. All 

 show cranio-caudal extensions. 



F. Reconstruction of Sparrow CO (= 6-day chick). Cranial-caudal extensions 



meet to form secondary sympathetic chain. 



G. lieconstruction of Sparrow B (= older than Sparrow 60). Secondary 



sympathetic chain formed. Connectives between primary and secondary 

 degenerating. 



C. Connective. D.R.G. Position of dorsal root ganglion. G.S. Gan- 

 glionic swelling. P.S.G. Viimavy sympathetic cord. M.C. iMedian connec- 

 tive. C.L.P. Constricted lateral process. L.F.C.C. Lateral processes with 

 cranio-caudal extensions. J. Junction of cranio-caudal extensions. S.S.C. 

 Secondary sympathetic chain. M.G. Median ganglia. B.C. J)cgencrating 

 connective. 



