THE CRANIAL NERVES. 333 



CHAPTER XVII. 



OF THE CRANIAL NERVES AND THE GREAT SYMPATHETIC. 



Enumeration of the Cranial Nerves. The Third Pair, or Oculo-motor. The Fourth Pair, orPa- 

 thetid. The Fifth Pair, or Trigemini. The Sixth Pair, or Abducentes. Illustrations of the 

 Third, Fourth, Fifth, and Sixth Pairs. The Seventh Pair, or Facial. Illustration of the 

 Facial. The Ninth Pair, or Glosso-pharyngeal. Illustration of the Glosso-pharyngeal. The 

 Tenth Pair, or Pneumogastric. Illustration of the Pneumogastric. Illustration of the Laryn- 

 geals. The Eleventh Pair, or Spinal Accessory. The Twelfth Pair, or Hypoglossal. Il- 

 lustration of the Hypoglossal. 



The Phrenic Nerve. 



Of the Great Sympathetic System. Position, Structure, and Origin of the Sympathetic. Its Re- 

 lation with the Pneumogastric. Its Connection with the Spinal System. Its Plexuses. Its 

 Ganglia. They are Reservoirs of Force. Summary of the Functions of the Sympathetic. 

 Illustration of the Sympathetic. The Abdominal Plexuses. The Solar Plexus. The Mesen- 

 teric Plexuses. 



THERE are twelve pairs of cranial nerves : 1st. The olfactory; 2d. The 

 optic ; 3d. The oculo-motor ; 4th. The pathetic ; 5th. The tri- The cranial 

 facial; 6th. The abducent ; 7th. The facial; 8th. The audito- nerves - 

 ry ; 9th. The glosso-pharyngeal ; 10th. The pneumogastric ; llth. The 

 spinal accessory ; 12th. The hypoglossal. 



Of these, the first, the second, and the eighth, being nerves of special 

 sensation, may be more conveniently studied in connection with the or- 

 gans of special sense the nose, the eye, the ear. 



OF THE THIRD PAIR, OR OCULO-MOTOR NERVES. 



The motor-oculi nerve arises from the inner side of the crus cerebri', 

 near to the pons varolii, some of its fibres passing into the The third pair, 

 gray substance of the crus. Advancing forward, it divides or oculo-motor. 

 into two branches, one of which supplies the superior rectus andlevator 

 palpebrae, the other the internal rectus, inferior rectus, and inferior ob- 

 lique. Considering the place of origin, it would be expected that this 

 nerve is wholly motor, and this is confirmed by experiment. When the 

 nerve is irritated the muscles which it supplies are convulsed, and when 

 it is divided they are paralyzed. Through its connection with the len- 

 ticular ganglion, it furnishes motor filaments to the iris. The optic 

 nerve, the corpora quadrigemina, and this nerve together constitute a 

 complete nervous arc, and impressions made on the retina occasion mo- 

 tions in the iris. 



