566 



OEIGIN OF NERVES. 



The first or olfactory nerve, or tract, is attached to the under 

 surface of the frontal lobe, in front of the anterior perforated space, 

 by three roots, named external, middle, and internal. 



The external or long root passes outwards as a band of white fibres, 

 along the anterior margin of the perforated space, towards the posterior 

 border of the fissure of Sylvius, where it disappears. Its fibres have 

 been traced by different observers to the island of Eeil, the optic 

 thalamus (Valentin), and to a nucleus in the substance of the temporo- 

 sphenoidal lobe, in front of the anterior extremity of the hippocampus 

 (Rolando, Luys, Foville). 



The middle or grey root is of pyramidal shape, and consists of grey 

 matter on the surface continuous with the adjacent grey substance of 

 the anterior perforated space. Within it are white fibres, which have 

 been said to go to the corpus striatum, or to join the fibres of the inner 

 root. 



Fig. 393. 



I ca 



Fig. 393. — View prom 



BELOW OP THE CONNEC- 

 TIONS OP THE Principal 

 Nerves with the 

 Brain (Allen Thomson). 



The full descriirtion of 

 this figure will be found at 

 page 534. The following 

 references a2)2)ly to the 

 roots of the nerves. 



I', the right olfactory 

 ti'act cut short and lying 

 in its groove ; II, the left 

 optic nerve in front of 

 the commissure, which is 

 concealed by the pituitaiy 

 body ih) ; II'. The left 

 tract is seen passing back 

 into e, the external, and ■/, 

 the internal corpus geni- 

 culatum ; III, the left 

 oculo-motor nerve ; IV, 

 the fourth or trochlear 

 nerve ; V, the greater root 

 of the fifth nerve ; + , the 

 lesser or motor root ; on 

 the right side this + is 

 jilaced on the Gasserian 

 ganglion ; VI, the sixth 

 nerve ; VII a, the facial 

 (the origin of which is 

 shown as extending down- 

 wards too far) ; VII b, the 

 auditory nerve ; VIII, the 

 pneiimo-gastric nerve ; 

 VIII a, the glosso-pharyn- 

 geal ; VIII b, the spinal 

 accessoiy nerve ; IX, the 

 hypoglossal nerve ; C I, 

 the first cervical nerve. 



With this fig. 385 may 

 be compared. 



The inner root, not always distinct, is composed of white fibres from 

 the inner and posterior part of the frontal lobe. They are said to be 



