BRACHIAL PLEXUS OF NERVES IN MAN 353 



sends a branch to the caudal trunk, plexus type A, so that this 

 nerve cannot be excluded from the medial anterior thoracic. In 

 3 cases it communicates with the medial^antibrachial cutaneous 

 nerve and in one with the intercostobrachial. 



In the other 22 instances where the nerve arises from the 

 medial fasciculus of the plexus it comes off from a stem common 

 to it and some other nerve, with the medial antibrachial cutaneous 

 in 8 instances; with the medial brachial cutaneous m 6, and 

 with both of these in 8 (fig. 1). 



In 32 of the 38 instances in which the medial anterior thoracic 

 nerve arises from the caudal trunk of the plexus, it is single and 

 in 6 it is from a stem, with the medial brachial cutaneous in 5 

 (fig. 11), and with both the medial brachial cutaneous and medial 

 antibrachial cutaneous in one (fig. 27). 



The eighth cervical and first thoracic nerves could neither of 

 them be excluded from the medial anterior thoracic nerve in 

 144 of the 151 satisfactory records, or 95.36 per cent. The 

 seventh and eighth cervical and first thoracic nerves may send 

 fibers in 4 cases, while the nerve receives fibers only from the 

 eighth in 3 instances. 



Herringham reports the medial anterior thoracic nerve as 

 receiving its fibers from the eighth cervical and first thoracic 

 nerves in 8 out of 10 cases. In the other two the eighth cervical 

 alone sent fibers to it. I found only 3 cases out of 151 in which 

 the first thoracic nerve failed to enter the plexus. It is possible 

 that some others if macerated would show that both nerves did 

 not enter into its formation, but this could not be proven by 

 dissection. In 3 cases the seventh cervical nerve positively 

 entered the nerve and in the plexus of type A it may have entered. 



THE LATERAL ANTERIOR THORACIC NERVE 



The lateral (external) anterior thoracic nerve is usually de- 

 scribed as arising from the cephalic trunk of the plexus. 



In my series there are 166 satisfactory cases. The nerve 

 arises by a single root in 39 instances, or in 23.49 per cent of the 

 cases; by two roots in 91, or 54.81 per cent; by three roots in 33, 

 or in 19.87 per cent; and by four roots in 3. 



