DISSECTING MANUAL. 



divisions of the fifth, sixth, seventh, and eighth cervical nerves 

 and most of the first thoracic ; it often gets a branch from the 

 fourth cervical and sometimes one from the second thoracic; 

 the latter always enters the intercosto-humeral. The fifth and 

 sixth cervical communicate with the middle cervical ganglion 

 of the sympathetic, and the seventh and eighth cervical with 

 the inferior ganglion. The plexus appears in the posterior 

 triangle between the Scaleni, anticus and medius. It quickly 

 unites in primary cords, the first cord being formed by the 

 fifth and sixth cervical, the second by the seventh cervical, 

 and the third by the eighth cervical and first thoracic. At the 

 same time each cervical nerve begins to divide into two trunks, 

 dorsal and ventral. The whole plexus is described with the 

 upper extremity. [622] 



Supraclavicular Branches. Anterior series: To (C. 5, 6, 7, 

 and 8; arising from them at the spinal foramina) the Scalenus 

 anticus and Longus colli. To (C. 5) the phrenic, but it may be 

 absent or of different origin. To (arising from the front of the 

 first cord) the Subclavius, crossing the subclavian artery. Pos- 

 terior series : To (C. 5, 6, 7, and 8, arising at the foramina) the 

 Scaleni, medius and posticus. The posterior scapular (arising 

 from the back of C. 5 at the foramen) pierces the Scalenus 

 medius and descends to the posterior border of the scapula. 

 The long thoracic (arising from the back of C. 5, 6, and 7 at the 

 foramina) pierces the Scalenus medius and descends behind 

 the plexus to the side of the chest. The suprascapular (arising 

 from the back of the first cord) descends above the plexus and 

 runs through the suprascapular foramen. [624] 



CRANIAL NERVES. 



Olfactory. About twenty nerves descend through the crib- 

 riform plate of the ethmoid to supply the upper part of the 

 nasal septum and the outer wall of the nasal fossa. [675] 



Ophthalmic. Terminal branches of the lachrymal supply 

 the conjunctiva and skin at the outer canthus of the eye; they 



[68] 



