BRACHIAL PLEXUS. 



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in the middle mediastinum by the side of the pericardium, 

 and is distributed to the diaphragm. 



2. Communicans noni, from second and third cervical ; 

 joins the descendens noni on the sheath of the cervical 

 vessels. 



3. Communicating, with cranial nerves. 



4. Muscular, to cervical muscles. 



The posterior division of the cervical nerves commu- 

 nicate but irregularly, and are distributed to the muscles 

 and integument at the back of the neck. 



Brachial Plexus. 



The brachial plexus rests upon the scalenus medius 

 muscle, and is formed by the anterior branches of the 

 fifth, sixth, seventh, and eighth cervical nerves and first 

 dorsal. In one hundred dissections of this plexus, made 

 during the last twelve years, and which were photo- 

 graphed, I do not find any two photographs alike. The 

 arrangement of the plexus can best be understood by the 

 following formula : 3 nerves + 2 nerves 2 trunks + 

 3 cords, or, briefly, 3N + 2N = 2T + 30. In ex- 

 planation, let it be remembered that five spinal nerves 

 enter into the brachial plexus ; that the fifth, sixth, and 

 seventh unite to form the upper trunk; and that the 

 eighth cervical and first dorsal unite to form the lower 

 trunk ; here we get 3N + 2N, which equals the sum 

 of 5. Draw a line through the plexus internal to the 

 two trunks formed by the five nerves, thus : 



Cords 



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