454 THE BRAIN 



The lateral root of the optic tract consists of fibres derived 

 from the retinae of both sides. They terminate partly in the 

 lateral geniculate body ; partly in the pulvinar ; and partly in 

 the superior colliculus of the same side, to which they pass 

 through the superior brachium. 



Pedunculi Cerebri (O.T. crura cerebri). The cerebral 

 peduncles constitute the chief bulk of the mesencephalon. 

 When the brain is viewed from below, they appear as two 

 large rope -like strands, which emerge, close together, from 

 the upper aspect of the pons, and diverge as they proceed 

 upwards and forwards to the cerebral hemispheres At the 



Corpus geniculatum mediale Superior brachium 



Pulvinar \ 1 Inferior brachium 



Superior quadrigeminal body 



Inferior 

 Stria terminalis fffi/^*' " AJ^LJ-/ / quadrigeminal body 



Corpus geniculatum tmi _. _ ; ^ 



laterale if~ ^Er "iT^"^ Aquaeductus cerebri 



Posterior perforated 

 substance 



Corpus mamillare 

 Tuber cinereum 



. 

 Anterior perforated 



^~9~ p ticchiasnia 



Optic nerve 



FIG. 179. The Origin arid Relations of the Optic Tract. 

 (Professor Thane, from Quain's Anatomy.} 



point where each peduncle disappears into the corresponding 

 hemisphere, it is embraced, on its lateral side, by the optic 

 tract and the gyrus hippocampi. 



Each pedunculus cerebri consists of two parts, viz., a 

 dorsal part, called the tegmentum, which is prolonged upwards 

 to the region below the thalamus ; and a ventral part, called 

 the basis (O.T. crusta\ which is carried upwards into a layer 

 of white fibres called the internal capsule, situated on the 

 lateral side of the thalamus. When the brain is examined 

 from below the bases of the peduncles are seen. They are 

 white in colour and streaked in the longitudinal direction. 

 On the exterior of the mesencephalon, the separation between 

 the two parts of the pedunculus cerebri (i.e. the tegmentum 



