THE DEEP CONNEXIONS OF THE CEEEBKAL NERVES. 607 



lemniscus. It is important to remember that the strise medullares are not always visible 

 in the floor of the fourth ventricle (Fig. 535), but are often buried more or less deeply. 



The connexion between the terminal cochlear nuclei and the inferior colliculus is 

 not altogether with that of the opposite side, as the foregoing description and the 

 diagram (Fig. 534) might lead one to infer. A few fibres pass directly to the inferior 

 colliculus of the same side, but none to the corresponding medial geniculate body : the 

 connexion with the latter is entirely crossed (Ferrier and Turner). 



From the medial geniculate body there proceeds a tract to the cerebral cortex of the 

 i transverse temporal gyri (Heschl's). The whole nervous apparatus is thus linked on 

 to the cerebral cortex, and the succession of neurones which build up the entire chain 

 are therefore: (1) in the cochlea of the internal ear, the bipolar cells of the spiral 



Lateral ventricle 

 Nucleus caudatus 

 Corona radiata 



Corpus callosum 



iternal capsule 



ustrum^ 



1 -alls) 



Thalamo-cerebral (sensory) 

 radiation in internal capsule 



Insula 



Acoustic 

 ^radiation enter- 

 ' ing transverse 

 temporal gyri 



Ventro-lateral thalamic nucleu 

 receiving the medial lemniscu 

 'and emitting sensory 

 fibres to the cortex 

 Acoustic radiation 

 Lateral geniculate body 

 receiving lateral lemniscus am 

 emitting acoustic radiation ; ~" 

 Lateral ventricle inferior corni 

 Medial geniculate body 

 Fimbria 

 Hippocampus 



K Lateral lemniscus 



Medial lemniscus at the part where 

 - the spinothalamic and bulbo- 

 thalamic tracts join 



p< nculi - 

 rebri 

 ibstantia - 



nigra 



^erebro-spinal and 

 >bro-pontine tracts 

 in the pons 



Nervus acusticus 

 rpus trapezoideum - 



Pyramid 



Decussation of pyramids 

 entral cerebro-spinal tract 



FIG. 537. A VERTICAL TRANSVERSE SECTION OF THE BRAIN TO SHOW THE WHOLE OF THE CENTRAL 

 ACOUSTIC PATH. The left hemisphere (right side of the figure) is cut on a plane posterior to that of 

 the right. Motor fibres red. Sensory fibres blue. Acoustic fibres yellow. 



ganglion emit axons that terminate in the brain ; in' (2) the cochlear nuclei, from the 

 nerve-cells of which fibres arise and cross to the lateral lemniscus of the opposite side, 

 proceeding to (3) the medial geniculate body, from which fibres pass to the cerebral cortex. 

 It must be borne in mind that all the axons of the cells of the superior olive do not 

 join the trapezoid strand.' Many leave its dorsal aspect and pass backwards in a group 

 called the pedicle of the superior olive, to end in the nucleus of the abducens nerve, 

 and, through the medial longitudinal bundle, in the nuclei of the trochlear and oculo- 

 motor nerves. In this way the organ of hearing is brought into connexion with the 

 iclei which preside over the movements of the eyeballs (Figs. 531, p. 599, and 536, p. 

 606). 



PEOSENCEPHALON OR FOEE-BRAIN. 



The fore-brain vesicle in the embryo has been subdivided, somewhat arbitrarily, 



