354 ABRAM T. KERR 



Of the' 39 plexuses in which it arises by a single root, this comes 

 from the cephalic trunk of the plexus in 2 (fig. 2), from the 

 ventral division of the cephalic trunk in 12 (fig. 4), from the 

 lateral fasciculus in 17 (fig. 21), from the seventh cervical nerve 

 in 2, and from the ventral division of the seventh cervical nerve 

 in 6. One of the nerves that arises from the lateral fasciculus 

 sends a branch to the medial head of the median nerve. 



In 73, or 78.02 per cent, of the 91 cases where the nerve arises 

 by two roots, one of these comes from the ventral division of the 

 cephalic trunk of the plexus and the second comes from the 

 ventral division of the seventh cervical nerve (fig. 3). In 7 

 cases both roots arise from the lateral fasciculus of the plexus 

 (fig. 20). One comes from the ventral division of the cephalic 

 trunk and one from the lateral fasciculus in 3 (fig. 11) ; one from 

 the ventral division of the sixth and one from the ventral division 

 of the seventh cervical nerve in 2. There is one instance of each 

 of the following: one branch from the ventral and one from the 

 dorsal division of the cephalic trunk, one from the lateral fascic- 

 ulus of the plexus and one from the seventh cervical nerve, both 

 from the seventh cervical, one from the seventh and one from the 

 dorsal division of the sixth cervical, one from the lateral fasciculus 

 of the plexus and one from the lateral head of the ulnar, one 

 from the lateral fasciculus and one from the combined cephalic 

 and intermediate trunks. 



In 18, or 54.54 per cent, of the 33 plexuses where there are 

 three roots to the lateral anterior thoracic nerve, one of these 

 arises from the ventral division of the cephalic trunk and the 

 other two from the ventral division of the intermediate trunk 

 (seventh cervical nerve) (fig. 1). In 5 cases one root comes from 

 the ventral division of the cephalic trunk, one from the lateral 

 fasciculus of the plexus and one from the seventh cervical nerve. 

 In 4 cases two roots come from the ventral division of the cephalic 

 trunk and one from the seventh cervical nerve, or its ventral 

 division. In 2 cases all three roots come from the lateral fascic- 

 ulus of the plexus. Each of the following arrangements is found 

 in one plexus only : one root from the ventral division of the fifth, 

 one from the ventral division of the sixth and one from the ventral 



