308 ABRAM T. KERR 



This variation is perhaps caused by the dissector removing less 

 than the usual amount of the connective tissue sheath that 

 surrounds the trunks but at the time of the dissection it appeared 

 as if as much had been removed as in other cases. 



In 14 plexuses the fifth and sixth cervical nerves divide into 

 dorsal and ventral branches and the ventral branches join to 

 form a cephalo- ventral trunk (fig. 15). In 2 cases the fifth 

 nerve divides into dorsal and ventral branches and the ventral 

 branch joins the sixth nerve to form the cephalic trunk, and in 

 2 others the sixth nerve divides into dorsal and ventral branches 

 and the ventral branch joins the fifth nerve to form the cephalic 

 trunk. The cephalic trunk in these cases divides into dorsal 

 and ventral divisions in the usual way. These cases are prob- 

 ably caused by the dissector removing more than the usual 

 amount of the connective tissue sheath from around the trunks. 



The intermediate trunk 



The intermediate trunk is formed by the seventh cervical 

 nerve only in all of the 175 cases. In 164 or 93.71 per cent it 

 ■divides into dorsal and ventral branches (fig. 1). The ventral 

 branch joins the ventral branches from the cephalic trunk or 

 nerves to form the lateral fasciculus and the dorsal division join- 

 ing the dorsal divisions of the cephalic and caudal trunks or 

 the nerves forming them to form the dorsal fasciculus or its 

 equivalent. 



In 5 instances the intermediate trunk divides into 3 parts. 

 In 4 of these, two of the divisions are ventral, one joining the 

 ventral branch of the cephalic trunk to form the lateral fascic- 

 ulus and the other passing to the medial fasciculus, while the 

 dorsal branch goes into the dorsal fasciculus in the usual way 

 (fig. 4). In the fifth instance there are two dorsal branches both 

 of which go to the dorsal fasciculus, and the ventral branch 

 joins the ventral branch of the cephalic trunk to form the lateral 

 fasciculus. In 4 other plexuses, already' noted in discussing 

 the cephalic trunk, the intermediate and cephalic trunks join 

 before dividing into dorsal and ventral branches (fig. 21). In 

 2 other cases the dorsal branch of the cephalic trunk joins the 



