340 ABRAM T. KERR 



In my series there are 172 plexuses in which the records are 

 satisfactory for the suprascapular nerve. In 108 or 62.79 per 

 cent of these it arises from the cephalic trunk of the plexus. 

 This trunk is formed by the union of the fourth, fifth and sixth 

 cervical nerves in 69 (fig. 6), and by the fifth and sixth in 39 

 (fig. 8). In 12 instances the suprascapular nerve arises from 

 the ventral branch of the cephalic trunk (fig. 12), and in only 

 1 of these the fourth cervical nerve fails to take part in the 

 formation of this trunk. In 22 instances the nerve arises from 

 the dorsal branch of the cephalic trunk and in 9 of these the 

 fourth cervical does not enter into the fonxiation of the brachial 

 plexus (figs. 3 and 7). 



In many cases it is very difficult to tell whether the supra- 

 scapular nerve arises from the cephalic trunk or from the dorsal 

 or ventral branch of it since it takes its origin just at the point 

 where the trunk divides into dorsal and ventral branches (fig. 

 11). In all cases I have considered it as arising from the trunk 

 unless it could be clearly shown that all of its fibers came from 

 either the dorsal or the ventral branch of the trunk. 



In 7 of the above 108 cases, the suprascapular nerve arises 

 from a common stem which in 5 divides into suprascapular and 

 subscapular nerves (fig. 5), and in one the stem divides into the 

 suprascapular nerve and a branch which joins the subscapular 

 nerve, while in the other case it arises from a similar common 

 stem which divides into the suprascapular nerve and the dorsal 

 scapular nerve to the rhomboid muscles. 



All 7 of the above exceptional cases belong to group 1, types 

 A and B of plexus. In 3 of the instances the branch arises from 

 the cephalic trunk; in 2 from the ventral branch of this trunk; 

 and in 2 from the dorsal branch of it. 



In 13 of the 172 plexuses studied the suprascapular nerve arises 

 from the trunk formed by the union of the fourth and fifth cer- 

 vical nerves (fig. 13). In one other case it comes from the 

 ventral branch of the above trunk and in another from the dorsal 

 branch of the trunk. In 14 instances it arises from the fifth cervi- 

 cal nerve alone (fig. 2) . In one of these latter the fourth cervical 

 nerve enters the plexus but the suprascapular arises high up in 



