THE MESENCEPHALON 



841 



which pass — (1) into the thalamus and to the telencephalon (prosencephalic continuation of the 

 cerebeUar path), and (2) fibres which descend into the spinal cord, the 'rubro-spinal tract,' 

 in the lateral funiculus (fig. 619). The latter cross from the red nucleus of the opposite 

 side and descend in the tegmentum. The red nuclei are also in relation with the fasciculus 

 retroflexus of Meynert, which belongs to the inter-brain. 



Fig. 664. — Scheme to Illustrate the Principal or Crossed Relations of the Descend- 

 ing Cortical^ (Pyramidal) Fibres to the Nuclei of Origin of the Cranial Nerves. 



Motor gyri of cerebral cortex 



Corona radiata 



Internal capsule 



• Cerebral peduncle 



■Nucleus of oculomotor nerve 



■Nucleus of trochlear nerve 

 Nucleus of mesencephalic 

 ' root of masticator nerve 



Chief nucleus of mas- 

 ticator nerve 



^.Nucleus of facial nerve 



.Nucleus of glosso-palatine 



nerve 

 'Nucleus of abducens 

 .Nucleus ambiguus 

 Dorsal efferent nucleus 

 of vagus 



^-■Nucleus of hypoglossal nerve 



•Nucleus of accessory nerve 

 • Decussation of the pyramids 



The thalamo -olivary tract courses in the mesencephalon more dorsally than in the pons 

 region. It rims in the ventro-lateral boundary of central grey substance just lateral to the 

 nuclei of the trochlear and oculomotor nerves. 



A small quadrigemino-po7itile strand of fibres has been described as arising in the quadri- 

 gemina, especially the inferior pair, and terminating in the nuclei of the pons. Impulses carried 

 by these fibres are probably destined for the cerebellar hemisphere of the opposite side. 



The superior quadrigeminate bodies (superior colliculi) are phj^logenetically 

 more important than the inferior. In certain of the lower vertebrates they are 



