CRANIAL NERVES. 



161 



1st. Olfactory. — Arises by three roots, which coalesce in the fis- 

 sure of Sylvius. 



2d. Optic. — Arises from the thalamus opticus and the tubercula 

 quadrigemina. 



3d. Motor Oculi. — Arises from the crus cerebri. 

 •4th. Patheticiis. — Arises from the valve of the brain. 



5th. Trifacial. — Arises from the medulla oblongata, but emerges 

 from the pons Varolii. 



6th. Motor Externus. — Arises from the corpus pyramidale. 



7th. Facial and Auditwy. — Arises from the corpus resti forme 

 and calamus scriptorius. 



8th. Fneunio gastric, glosso-pharyngeal, and spinal accessory. — 

 Arises by filaments from the fissure between the corpora olivare and 

 restiforme, and from the spinal cord opposite the fourth cervical 

 vertebra. 



9th. Hypoglossal. -^Arises in the fissure between the corpus py- 

 ramidale and corpus olivare. 



The cranial nerves may be divided into three classes, according 

 to their function, viz.: — Nerves of special sense, including the 1st, 

 2d, and the auditory branch of the 7th. Nerves of motion, including 

 the 3d, 4th, 6th, facial branch of the 7th and 9th. Compound 

 nerves, comprising the 8th and 5th. 



The distribution of the cranial nerves — 



1st. Olfactory. — Forms a large soft bulb, which rests on the cribri- 

 form plate, and sends filaments through its foramina to the Schneide- 

 rian membrane. 



2d. Optic. — Forms a chiasm with its fellow, and enters the globe' 

 of the eye to join the retina. Is a flattened cord. 



3d. Motor Oculi? — Passes through the walls of the cavernous 

 sinus to escape at the sphenoi- 



dal foramen, and then is dis- 

 tributed upon the muscles of 

 the eyeball, with the exception 

 of the superior oblique and 

 external rectus. It sends a 

 branch to join the ophthalmic 

 ganglion, from which proceed 

 the ciliary nerves,^ which sup- 

 ply the iris. 



4th. Pathetic. — Passing 

 through the walls of the caver- 

 nous sinus, and through the 

 sphenoidal foramen, it is distri- 

 buted upon the superior ob- 

 lique muscles of the eyeball. It 

 is the smallest cranial nerve. 



6th. Motor Externus. — 



Fig. 140. 



14* 



