BEACHIAL PLEXUS OF NERVES IN MAN 369 



the diameter is dependent upon so many other factors than the 

 nerve fibers. 



8. Maceration shows how very complexly the nerve bundles 

 interlace and join and how difficult it is, even when the epineurium 

 is removed by maceration, to trace the bundles. 



9. By anatomical methods the fibers of a given spinal nerve 

 can rarely be traced through the plexus to their ultimate dis- 

 tribution. In only a few of the branches of the plexus can it be 

 determined anatomically which spinal nerves send fibers to them. 



10. The nerves cephalic to the seventh cervical join to form a 

 cephalic trunk which then divides into dorsal and ventral branches 

 in nearly 90 per cent of the cases. 



11. The nerves caudal to the seventh unite to form a caudal 

 trunk in over 95 per cent of the plexuses. 



12. The seventh cervical remains single and forms the inter- 

 mediate trunk in all cases. 



13. In over 80 per cent of the cases the lateral fasciculus is 

 formed by the union of the ventral branches of the cephalic and 

 intermediate trunks. 



14. The medial fasciculus is composed of the ventral branch 

 of the caudal trunk in over 95 per cent of the plexuses. 



15. In nearly 70 per cent of the plexuses the posterior fasciculus 

 is formed by the union of the dorsal divisions of the cephalic, 

 intermediate and caudal trunks. In over 20 per cent of the 

 plexuses there is no true posterior fasciculus formed. 



16. The plexuses are subdivided into seven subgroups or types 

 based upon the nerves entering the medial or the lateral fasciculus. 



17. In type A, group 1, the fourth cervical nerve sends a 

 branch to the plexus and the seventh cervical nerve gives a branch 

 to the medial fasciculus. There are less than 3 per cent of the 

 plexuses of this type (fig. 4) . 



18. In type B, group 1, the fourth cervical nerve sends a branch 

 to the plexus and the medial fasciculus receives no branch from 

 the seventh cervical nerve. Over 57 per cent of the plexuses 

 are of this type (fig. 1). 



19. Type C, group 1, differs from the preceding in having a 

 branch from the caudal trunk or eighth cervical nerve to the 



