314 ABRAM T. KERR 



thoracic. I do not believe that with my material this point could 

 have been determined in the majority of plexuses. 



SUBDIVISIONS OF THE PLEXUSES OF GROUPS 1, 2 AND 3 



The lateral fasciculus of the plexus or its equivalent contains 

 fibers from the seventh cervical and the nerves cephalic to this 

 and the medial fasciculus contains fibers from the eighth cervical 

 and the nerves caudal to this in 164 or 93.71 per cent of the 175 

 plexuses studied. Some of the 11 atypical specimens are found 

 in each of the three groups into which the plexuses are divided. 

 In 6 of the 11 atypical specimens there is a brajich from the 

 intermediate trunk (seventh cervical nerve) to join the caudal 

 trunk or the medial fasciculus of the plexus (fig. 4). In the other 

 5 there is a branch from the caudal trunk or the eighth cervical 

 nerve to join the lateral fasciculus or one of the nerves that go 

 to it (figs. 6 and 8). 



The branch to the lateral fasciculus is found in the plexuses of 

 group 1 and 3 but has not been found among those of group 2. 

 The branch from the intermediate trunk to the medial fasciculus 

 has been found among groups 1 and 2. 



Schumacher describes in 8 of the 10 cases examined by him a 

 branch from the lateral to the medial fasciculus. He may refer 

 to a branch similar to the one mentioned above from the inter- 

 mediate trunk to the medial fasciculus or to a branch similar to 

 the lateral head of the ulnar nerve. 



It is not improbable that the significance of this branch to the 

 medial fasciculus may be the same as that of the lateral head of 

 the ulnar nerve, although in one case the two coexist. Its sole 

 function might be to bring fibers of the seventh cervical or some 

 nerve cephalic to this to the ulnar nerve. 



The lateral head of the ulnar nerve occurs in 75 plexuses or in 

 42.85 per cent of the 175. Fifty-five of these are in group 1 or 

 50.00 per cent of the 110 plexuses in the group. Sixteen are in 

 group 2 or 30.76 per cent of the 52 plexuses of this group and 4 

 are in group 3 or in 30.76 per cent of the 13 plexuses found here. 

 It will be seen then that this also occurs more often in the cephalic 

 group of plexuses. A more detailed description of this lateral 



