368 ABEAM T. KERR 



21 cases; the seventh and eighth in 13; sixth, seventh and eighth 

 in one; the sixth, and seventh in 3; the fifth, sixth and seventh 

 in 3 and the fifth, and sixth in one case. It will be noted that 

 from only one case in his series was the seventh lacking. In 

 my series there are 4 cases in which the seventh cervical nerve 

 does not enter the thoracodorsal nerve. In 3 of these it comes 

 from the fifth and sixth cervical nerve as in Herringham's case 

 and in the other case from the eighth cervical and first thoracic 

 nerves. 



SUMMARY 



1. The 175 brachial plexuses studied can be divided into three 

 groups according to the nerves joining the cephalic border of the 

 plexus. 



2. Those plexuses that receive a branch from the fourth cervi- 

 cal nerve are grouped together as group 1. Over 62 per cent of 

 the plexuses are formed in this way (fig. 1). 



3. Those plexuses that receive no branch from the fourth cervi- 

 cal nerve but in which the whole of the ventral division of the 

 fifth cervical nerve joins the plexus form a second group. Nearly 

 30 per cent of those studied are in this group (fig. 2). 



4. Plexuses that receive no branch from the fourth cervical 

 and in which a part of the fifth cervical nerve helps to form the 

 cervical plexus form a third group that contains a little over 7 

 per cent of the plexuses (fig. 3). 



5. The plexuses studied do not show that sex, color or side 

 of the body have much if any influence upon the classification 

 into these groups. 



6. Plexuses that receive a branch from the fourth cervical 

 nerve are more cephalic as regards the spinal column and those 

 in which only part of the fifth enters the plexus are more caudal. 

 The larger the branch from the fourth nerve to the brachial plexus 

 the more cephalic the plexus and conversely, the larger the branch 

 from the fifth to the cervical plexus, the more caudal the plexus. 



7. The relative size of the nerves, especially those in the center 

 of the plexus, is found to have but little value in estimating the 

 position of the plexus as cephalic or caudal. This is because 



