Chap, 28.] Cervical Nerves. 289 



of the head which pafs down to the neck. They are 

 afterwards chiefly fpent on the extenfors of the head, 

 the levators of the fcapulse, and the neighbouring in- 

 teguments. 



The third cervical nerve paffes from the fpinal mar- 

 row, between the third and fourth vertebras, and join- 

 ing with the fourth cervical, forms the phrenic nerve, 

 which pafTes down by the fubclavian veflels in its way 

 to the diaphragm, on which it is expended. The 

 other branches of the third pair are diftributed to the 

 mufcles of the neck and top of the moulder. Hence 

 it has been attempted to account for the pain at the top 

 of the right fhoulder in inflammations of the liver. 

 The diaphragm is fuppofecj to be affecled either by 

 its contacl: with the liver, or by the increafed weight of 

 that vifcus pulling it downwards j and the ihoulder is 

 thought to fympathize with the diaphragm, becaufe it 

 receives nerves from the fame fource. This expla- 

 nation, however, is very unfatisfaclory, fince nothing 

 is more common than for parts to be fupplied by the 

 fame serves without having any fuch fympathy. 



The fourth cervical nerve, after having given of? 

 that branch which joins with tl)e third to form the 

 phrenic, pafles to the axilla, where it forms a plexus 

 with the fifth, fixth, and feventh cervical nerves, and 

 with the firft of the dorfal. After giving feveral con- 

 fiderable nerves which are diftributed on the mufcles of 

 the thorax, they form feveral branches which pafs 

 down on the arm, and fupply the whole fuperior ex- 

 tremity. 



The dorfal nerves are twelve in number, and aU 

 contribute to the formation of the great intercoftal. 

 The firft of the dorfal nerves differs frpm the reft in 

 contributing to the formation of the brachial nerves, 



VOL.]!!. U -and 



