CONXECTION WITH THE BRAIN. 



521 



The deep connection or origin of these nerves is still in some cases a 

 matter of considerable uncertainty. Where they can be followed, the 

 fibres may be traced to, and probably in part arise from, certain col- 

 lections of grey substance termed "nuclei." These nuclei are further 

 connected by other fibres with each other and with the cerebral hemi- 

 spheres. The deep origin of the first or olfactory nerves is still doubt- 

 ful ; the second pair are connected chiefly with tlie optic thalami and 

 corpora quadrigemina ; the third and fourth with a nucleus deeply 

 placed beneath the corpora quadrigemina ; the remainder with a con- 

 tinuous series of collections of grey matter which lie beneath the floor of 

 the fourth ventricle and in the central part of the medulla oblongata, 

 around the central canal, as low down as the decussation of the 

 pyramids. 



Fig. 329. 



Fig. 329. — Lateral View of the Connection op the Principal Nerves with the 



Brain. (A. T. ) 

 The full description of this figure will be found at p. 550, vol. ii. 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 {Tli), corpora geniculata [i, c), and corpora quadrigemina (q) ; III, 

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

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

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

 glosso-phai7ngeal, pneumo-gastric, and spinal accessory nerves ; IX, the hypoglossal 

 nerve ; C I, the separate anterior and posterior roots of the suboccipital nerve. 



