636 



TEXT-BOOK OF PHYSIOLOGY 



Properties. Stimulation of the nerve-trunk is followed by spasmodic 

 contraction of the superior oblique muscle, the anterior pole of the eyeball 

 being turned downward and outward, combined with slight torsion away 

 from the middle line. 



Division of the nerve is followed by a relaxation or paralysis of the 

 muscle. In consequence of the now unopposed action of the inferior 

 oblique muscle, the anterior pole of the eyeball is turned upward and in- 

 ward with slight torsion toward the middle line. The diplopia consequent 

 upon this paralysis is homonymous, the images appearing one above the 

 other. The image of the paralyzed eye is below that of the normal eye and 

 its upper end inclined toward that of the normal eye. 



Function. The function of the trochlear nerve is to transmit nerve 

 impulses to the superior oblique muscle and to excite it to contraction. 



THE FIFTH NERVE. THE TRIGEMINAL 



The fifth cranial nerve, the trigeminal, consists of both afferent and 

 efferent axons which for the most part are separate and distinct. The 



afferent axons constitute 

 by far the major portion, 

 the efferent fibers the 

 minor portion, of the 

 nerve. 



Origin of the Affer- 

 ent Axons. The afferent 

 axons have their origin 

 in the monaxonic cells in 

 the ganglion of Gasser, 

 which rests on the apex of 

 the petrous portion of the 

 temporal bone. The cells 

 of this ganglion give origin 

 to a short process which 

 soon divides into two 

 branches, one of which 



FIG. 2 6 5 .-ScHEME OF ORIGIN AND CONSTITUTION OF THE P as . se f centrally, the Other 

 TRIGEMIXAL NERVE, i. Centrally coursing fibers. 2, 3, peripherally (Fig. 265). 

 4. Peripherally coursing fibers of the cells of the ganglion of The Centrally directed 

 Gasser. R t N. Nuclei of origin of the efferent fibers. 6. v i ^1lJL*:.1 r f^r- 



Motor root. Central terminations of the large root. branches Collectively iorm 



the so-called large or sen- 

 sor root; the peripherally directed branches collectively constitute the three 

 main divisions of the nerve: viz., the ophthalmic, the superior maxillary, 

 and the inferior maxillary. Branches of the carotid plexus of the sym- 

 pathetic enter the nerve in the neighborhood of the ganglion of Gasser and 

 accompany some of its branches to their terminations. 



Distribution. i. The Central Branches. The axons of the large root 

 pass backward into the pons Varolii on its lateral aspect. After entering 

 the pons each axon divides into two branches, one of which passes upward 

 a short distance, the other passes downward, descending as far as the 

 second cervical segment. Both branches give off a number of collaterals, 



