BRACHIAL PLEXUS OF NERVES IN MAN 301 



plexus of the strongest elements, that is, the nerves with the 

 greatest diameters. 



I have attempted in 27 cases to classify the plexuses in this 

 way, table 11. The anterior rami of the spinal nerves entering 

 the plexus were measured as soon as the surrounding connective 

 tissue was removed. The measurement was made while the 

 plexus was still connected to the spinal cord, that is, before the 

 upper extremity was separated from the body. The diameters 

 were taken with sharp pointed dividers and the measurements 

 were recorded by sticking the points of the dividers into the 

 paper, upon which the diagram of the plexus was made. 



Twenty-one of the plexuses are in group 1, and receive a branch 

 from the fourth cervical nerve. This is the smallest branch 

 entering the plexus, it being remembered that the branch from 

 the second thoracic is not considered. 



If we disregard the fourth cervical, the smallest nerve entering 

 the plexus is the fifth cervical in 11 instances, and fifth cervical 

 and the first thoracic equally in 9, and the first thoracic in 7. In 

 the 11 cases where the fifth cervical is the smallest, the first 

 thoracic is next in size — the sixth is equally large in 3 of these, 

 the sixth, seventh and eighth in 1 and the seventh in 1. In the 

 7 instances in which the first thoracic is the smallest nerve, the 

 fifth cervical is the next in size in 5, in two of which the eighth 

 is equally small. The sixth cervical is the nerve of second size 

 in 1 and the eighth in 1 . 



In the 27 cases, the nerves with the greatest diameter entering 

 the plexus are the seventh cervical nerve in 7 cases, 5 in group 1, 

 2 in group 3; the eighth cervical nerve in 6 cases, 5 in group 1, 

 1 in group 3; and the sixth cervical nerve in 2, 1 each in groups 1 

 and 2. The seventh and eighth cervical nerves are equal in 

 diameter and are the largest nerves in 6 cases, 5 in group 1 and 

 1 in group 2; the sixth, seventh and eighth cervical are equal and 

 largest in 2 cases both in group 1 ; the first thoracic, sixth, seventh 

 and eighth cervical nerves are equal and the largest in one instance 

 in group 3; the sixth and seventh cervical nerves are equal and 

 are the largest nerves in 2 cases, both in group 1 ; and the fifth, 

 sixth and seventh are largest and equal in one instance in group 2. 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 23, NO. 2 



