326 ABRAM T. KERR 



Through the lateral head of the ulnar there is brought to the 

 ulnar nerve fibers from the seventh cervical nerve and, in cases 

 where the branch arises from the lateral fasciculus of the plexus 

 or from the lateral head of the median nerve, the possibility of 

 fibers from the sixth, fifth and fourth cervical nerves, one or all, 

 entering the ulnar nerve cannot be excluded. Since this branch 

 brings to the ulnar nerve fibers from the seventh cervical nerve, 

 we might expect to find it absent in those cases in which these 

 fibers may be obtained in another way, for example, in those 

 cases in which the seventh cervical nerve sends a branch to the 

 medial fasciculus of the plexus as in plexuses of types A and D. 

 In 5 of the plexuses of these two types there is no lateral head 

 to the ulnar nerve. In one plexus of type A, there is however 

 also a lateral head to the ulnar nerve (fig. 12), but in this case it 

 arises from the lateral fasciculus of the plexus and may contain 

 fibers from some of the nerves cephalic to the seventh cervical. 

 It is suggestive that the branch from the seventh cervical nerve 

 to the medial fasciculus in the 6 plexuses of types A and D 

 represents the lateral head of the ulnar arising more proximally 

 than usual although in three of the 6 instances the fibers of the 

 seventh cervical nerve cannot be excluded from one of the other 

 branches of the plexus. 



In the 5 atypical cases in which the medial fasciculus joins 

 the lateral or the lateral head of the median before the ulnar 

 nerve is given off, the ulnar may receive fibers from any of the 

 nerves cephalic to the eighth cervical. If we disregard the 30 . 

 cases in which a branch similar to the lateral head of the ulnar 

 is present but ends in the medial head of the median nerve and 

 that I have considered as a possible broken branch, we have 145 

 plexuses in which the record is positive. Among these the 

 ulnar nerve is formed of fibers of the eighth cervical and first 

 thoracic nerves in 61 or 42.06 per cent and of fibers from the 

 seventh and eighth cervical and first thoracic in 16 or 11.03 per 

 cent. In the remaining 68 cases or 46.89 per cent the ulnar has 

 a lateral head that comes from the lateral fasciculus of the 

 plexus, or from the lateral head of the median, and it is not 

 possible to say if the fibers are from the seventh cervical alone 



