484 THE ORGANS 



B. Efferent Mesencephalic 



XV. CoUicuIo-bulbar and coUiculo-spinal (crossed) + cranial (especially VII 

 for squint reflex) and spinal peripheral motor neurones. (Fig. 35S.) 



XVI. CoUiculo-medial longitudinal fasciculus: This path probably consists 

 of coUicular neurones which pass to the nucleus of the medial longitudinal fascic- 

 ulus + the latter nucleus and its descending axones in the medial longitudinal 

 fasciculus + peripheral motor neurones of brain (especially oculomotor) and 

 cord. (Fig. 358.) 



Inasmuch as the superior coUiculus receives optic fibres, paths XV and XVI 

 are probably largely concerned in optic reflexes. 



C. Efferent Cerebellar 



XVII. Cerebellar cortico (cortex of cerebellar hemispheres) — dentate -f 

 dentato-rubral (superior cerebellar peduncle, crossed) + rubro-spinal (crossed) 

 + peripheral motor neurones. (Figs. 331, 345.) 



XVIII. Cerebellar cortico (cortex of vermis) — fastigial + fastigio — Deiters 

 (mesial part of inferior cerebellar peduncle) + Deitero-bulbar and Deitero-spinal 

 (crossed and uncrossed) -j- peripheral oculomotor and spinal motor neurones. 

 (Figs. 331, 339.) 



Inasmuch as Deiters' nucleus also receives directly vestibular nerve fibres, 

 there exists the important vestibulo-Deiters + Deitero-bulbar and Deitero-spinal 

 -f peripheral motor neurones reflex path whereby the vestibulo-semicircular canal 

 receptors directly influence the position of eyes and body. 



Aft'erent pallial path \TI is obviously also an efferent cerebellar path. (Figs. 



331, 345-) 



The large efferent pallial paths XI and XIII markedly affect the configura- 

 tion of the brain. These two paths are added ventraUy to the segmental and 

 intersegmental apparatus and form the pes pedunculi or crusta (added ventraUy 

 to the tegmentum of the midbrain), the pons \'arolii (added ventraUy to the teg- 

 mentum of midbrain, isthmus and hindbrain) and the pyramids (added ventraUy 

 to the hindbrain). Arising from the neopaUium (p. 538), they are to be regarded 

 as largely more recent acquisitions by the vertebrate nervous system. 



SUPRASEGMENTAL STRUCTURES • 



These are the pallium or cerebral hemispheres, the inferior and 

 superior colliculi or corpora quadrigemina and the cerebellum. 

 They consist essentially of the endings and beginnings of their re- 

 spective afferent and efferent paths and of their own association 

 neurones, the bodies of which lie in their respective cortices. 



The corpora quadrigemina are relatively of much less importance in the 

 human brain. 



In accorda.nce with the above there are usually to be distinguished 

 in transverse sections of the brain at various levels the following: 



