348 NERVOUS SYSTExM. 



2. A large branch to the senatus magnus. 3. The most impor- 

 tant of the three, takes a deep-seated course to the point of the 

 shoulder : there it sends off — a. A filament to the phrenic nerve. 

 b. One of communication to the sixth cervical nerve, c. One 

 that descends obliquely outward to contribute to the formation 

 of the humeral plexus. 



Sixth Cervical Nerve 

 At its exit, bifurcates. The superior J'ascis, comparatively 

 small, turns round the articulation, runs upward, and penetrates 

 the serratus inagnus. — The inferior fascis, remarkable for the 

 number and large size of its branches, passes backward un- 

 der the transverse process of the seventh vertebra. It furnishes — 

 1. Twigs to the longus colli. 2. A loig filament to the /?os^er?"o/' 

 cervical ganglion . 3. A filament to the phrenic nerve. 4. Large 

 branches running to the formation of the humeral plexus. 



Sevoith Cervical Nerve. 

 The last of these nerves comes out between the last cervical 

 vertebra and the first dorsal. Its superior fascis, very incon- 

 siderable, consists of a small branch only which is expended in 

 the serratus magnus. — The inferior J'ascis comprises a large, 

 flat nerve, directed backward to join the hunieral plexus. In its 

 way, it forms a broad union with the first of the dorsal nerves, 

 and detaches a branch to the sympathetic nerve. 



The Diaphragmatic, or Phrenic Nerve, 

 Principally formed by the union of branches from the fifth and 

 sixth cervical nerves, and generally by the addition of a small 

 filament from the fourth, takes a solitary course down the neck, 

 along the inferior border of the scalenus, enters the thorax just 

 above the root of the axillary artery, and traverses the side of 

 the pericardium to reach the tendinous centre of the diaphragm, 

 where it divides and spreads out into many divergent rami- 

 fications. 



Dorsal Nerves. 

 Of these nerves there are eighteen pah's. In issuing from the 

 spine they are directed obliquely backward. Like the cervical 

 nerves, they are regularly numbered in succession ; and present, 

 at their exit, superior and inferior fasces ; but the fasces 

 are less in size, and evolve fewer ramifications. The hferiur 

 branches acquire the name of intercostal nerves; because they 

 correspond with the intercostal bloodvessels, which they accom- 

 pany along the shallow furrows in the posterior edges of the ribs, 

 between the internal and external intercostal muscles, directing 

 their course to the steinum. 



