ROOTS OF THE CEAXIAL NERVES. OPTIC. 



585 



same side : the inner fibres cross over to the opposite side ; and fibres have 

 been described as running from one optic tract to the other along the 

 posterior part of the commissure, while others pass between the two optic 

 nerves in its anterior part (Mayo). 



In front of the commissure, the nerve enters the foramen opticum, 

 receiving a sheath from the dura mater and acquiring greater firmness. 



Fig. 398. 



Fig. 398. LATERAL VIEW OF THE CONNECTION OP THE PRINCIPAL NERVES WITH THE 



BRAIN. 



The full description of this figure will be found at p. 553. The following references 

 apply to the roots of the nerves ; I, the right olfactory tract cut near its middle ; II, the 

 optic nerves immediately in front of the commissure ; the right optic tract is seen passing 

 back to the thalamus (Th\ corpora geniculata (i, e,), and corpora quadrigemina (5) ; III, 

 the right oculo-motor nerve ; IV, the trochlear nerve rising at v, from near the valve of 

 Vieussens ; V, the trifacial nerve ; VI, the abducent ocular ; a, VII, &, the facial and 

 auditory nerves, and between them the pars intermedia ; a, VIII, b, the roots of the 

 glosso-pharyngeal, pneu mo-gastric, and spinal accessory nerves ; IX, the hypoglossal 

 nerve ; C I, the separate anterior and posterior roots of the suboccipital or first cervical 



The fibres of origin of the optic tract from the thalamus are derived partly from the 

 superficial stratum and partly from the interior of that body. According to Foville, 

 this tract is also connected with the tsenia semicircularis, and with the termination 

 of the gyrus fornicatus ; and he states further, that where the optic tract turns round 

 the back of the thalamus and the cerebral peduncle it receives other delicate fibres, 

 which descend from the grey matter of those parts. (Op. cit. p. 514.) 



Q Q 



