SYSTEM AND SUPUAUENAL BODIES IN THE SPARROW. 767 



Apax'fc from thein the primary cords are so reduced, by the 

 migration above described, that they may be considered to be 

 wholly absorbed by the definitive sympathetic nervous system. 

 It should be stated that the primary sympathetic chain contri- 

 butes also to the formation of coeliac and other ganglia, thus the 

 degeneration of the primary sympathetic chains, described by 

 previous writers, shoukl rather be termed a migration from the 

 primary location. 



We are unable to assign a cause for this migration of the 

 primary sympathetic chains from the dorso-lateral angles of the 

 aorta to their definitive position, as secondary sympathetic chains 

 in the vertebrarterial canal. Thcbault, in his description of the 

 sympatlietic system in adult birds, suggests tliat the long thin 

 neck of the bird renders the sympathetic liable to lesions; hence 

 he explains its inclusion in the vertebrarterial canal. If this be 

 the case, we may regard the definitive location as an adaptive 

 modification. It is perhaps worth notice that the reptile in 

 Avhich primary and secondary sympathetic chaiuH have also been 

 described, viz. the tortoise, is also endowed Avith a long and 

 flexible neck. 



In conclusion, we would express our gratitude to Professor 

 J. P. Hill, F.R.S., for his generosity in supplying us Avith such 

 an abundance of excellent material and for much assistance in 

 the course of our work and in the preparation of this paper. 

 We are indebted to Professor D. M. S. Watson, F.R.S., for 

 friendly criticism and for aid in final preparation for the press. 



I. Sumjnary. 



1. The primary sympathetic primordia originate from the 

 spinal cord, and are hence ectodermal in origin. 



2. The primordia of the ganglia of the primary sympathetic 

 chain are laid down metamerically at inter-somitic points. 



,'}. The constituent cells of the primordia are derived from 



a. The neural crest ; 



b. The dorsal root ganglia ; 



c. The neural tube by way of the ventral root. 



4. The primordia extend cranially and caudally to form a 

 continuous chain on either side. 



5. The primary ganglionic swellings extend dorso-latcrally. 

 The free ends of these extensions enlarge and becoming sepa- 

 rated from the primary ganglia give origin to the definitive 

 sympathetic ganglia. 



6. As in the case of the primary ganglia these definitive ganglia 

 extend cranio-caudall)' and unite to form a continuous chain. 



7. The primary S3'mpathetic gives origin to 



a. The secondary sympathetic chains ; 



b. The chromaffin cells of the medulla of the supra- 



renal body ; 



c. The cceliac and other ganglia; 



d. The unpaired ganglia in the cervical region. 



