82 ANATOMY OF THE HEAD AND NECK. 



responding to the anterior border of the cerebellum. Th< 

 convexity of the cerebrum shows no marks of the subdiv 

 sion into lobes. 



ORIGINS OF THE CRANIAL NERVES. 



The CRANIAL NERVES, with the exception of the spin? 

 accessory, have their origin in the encephalon and p 

 through apertures in the skull. The origin of a nerve i* 

 described as either apparent or deep, the former term r< 

 ferring to the point at which it appears superficially, an< 

 the latter to its commencement in the nervous substan< 

 The apparent origin of the nerves will alone be given. 



The FIRST, or OLFACTORY NERVE, lies in a sulcus on th< 

 under surface of the anterior lobe of the cerebrum ; it i; 

 prismatic in form, and terminates anteriorly in a bull 

 posteriorly it is connected with the cerebrum by thn 

 roots : an inner root, not always apparent, from the mm 

 part of the anterior lobe, a middle root from the posterioi 

 part of the sulcus in which the nerve lies, and an exterm 

 root from the posterior lip of the fissure of Sylvius. 



To see the middle root, the nerve must be reflected and examim 

 from its deep surface. 



- The SECOND, or OPTIC NERVE, is the largest of the crani 

 nerves. Anteriorly the nerves of the two sides unite an 

 form the optic commissure, or chiasma ; behind the co 

 fnissure the nerve is called the optic tract ; it winds aroun 

 the crus cerebri, and splits into two parts, which may 

 traced back to the optic thalamus and the corpora quad 

 gemina. 



The THIRD, or MOTOR OCULI NERVE, arises just in front 

 of the pons Yarolii, near the locus perforatus, from th 

 inner side of the crus cerebri. 



The FOURTH, or TROCHLEARIS NERVE, the smallest of th 

 cranial nerves, emerges between the cerebrum and cerebe 

 him at the outer side of the crus cerebri, round which 

 winds. It may be traced to the valve of Yieussens. 



The FIFTH, or TRIFACIAL NERVE, springs from the side 

 of the pons Varolii near its anterior border, where it 

 emerges as two roots, separated from each other by a slight 

 interval. 



The SIXTH, or ABDUCENS NERVE, springs from the upper 

 part of the corpus pyramidal e of the medulla oblongata, 

 close behind the posterior border of the pons Yarolii. 



it 







