958 



THE NERVE SYSTEM 



and end, contralaterally, in relation with the facial and hypoglossal nerve nuclei 

 (also called the emissary speech tract). 



The corticospinal division arises from the remainder of the motor area, courses 

 through the frontal two-thirds of the internal capsule, through crusta, pons, and 

 medulla oblongata, to form the pyramids, and, undergoing partial decussation, 

 forms the direct and the crossed pyramidal tracts described in the spinal cord. 



(b) The frontopontile tract (Arnold's bundle) arises in the midfrontal cortex, 

 courses through the internal capsule (caudal part of frontal limb), forms the mesal 

 sector (one-fifth) of the crusta, and ends in the nuclei pontis. 



(c) The temporopontile tract (Tiirck's bundle) arises in the cortex of the tem- 

 poral lobe, descends through the internal capsule (caudal segment), forms the 

 ectal (one-fifth) sector of the crusta, and ends in the nuclei pontis. The existence 

 of occipitopontile fibres is denied by Archambault in a recent contribution (1906). 



(d) The occipitomesencephalic tract arises in the visual area (cuneus and cal- 

 carine formation), courses through the retrolenticular part of the internal capsule, 

 to end in the superior quadrigeminal body and in relation with the nuclei for move- 

 ments of the eyeball. 



(e) Part of the fibres composing the optic radiation are corticipetal, arising in 

 the occipital cortex and ending in the pulvinar of the thalamus and the external 

 geniculate body. 



CENTRIFUGAL FIBRE 

 TERMINATING IN BULB 



OLFACTORY 

 GLOMERULI 



OLFACTORY. 

 MUCOSA 



FIG. 711. Schema of the olfactory bulb and tract neurones. 



2. Ascending (corticipetal) tracts arise mostly from the nuclei of the thalamus 

 and hypothalamus, mid-brain, and cerebellum. 



(a) The terminal or cerebral part of the general sensor pathway of the body 

 comprises the axones arising in the cells of the lateral nucleus of the thalamus 

 and the hypothalamic nucleus interposed way-stations which transfer the im- 

 pressions carried along the medial lemniscus from the nuclei of the gracile and 

 cuneate fasciculi in the myeloblongata transition. They convey sensor impres- 

 sions from the body periphery to the somesthetic area of the cortex chiefly the 

 postcentral and parietal gyres. 



(b) The terminal or cerebral part of the general sensor pathway of the head and 

 neck comprises the axones which arise from the afferent cranial nerve nuclei 

 (excepting the auditory) and course along the medial lemniscus to the thalamus 

 and hypothalamic nucleus, to be thence projected to the somesthetic cerebral 

 cortex. 



(c) The terminal or cerebral part of the auditory pathway from the inferior quadri- 

 geminal body, internal geniculate body, and the interposed nucleus of the lateral 

 lemniscus, ending in the auditory sphere of the cerebral cortex. 



(d) The terminal part of the visual pathway, described on page 911. 



