CEEEBKAL CONNEXIONS OF THE OPTIC TRACT. 



619 



CEREBRAL CONNEXIONS OF THE OPTIC TRACT. 



The optic nerve is connected with the hypothalamus. At the optic 

 jhiasma the optic nerves of the two sides are joined together and a partial 

 lecussation of fibres takes place. The fibres which arise in the medial half of each 

 .-etina cross the median plane and join the optic tract of the opposite side. The 

 ')ptic tract proceeds backwards round the cerebral peduncle, and in the neighbour- 

 lood of the geniculate bodies appears to divide into two roots, viz., a lateral and 

 i medial (Fig. 546), but only the former is really part of the tract. 



Commissure of Gudden. The so-called medial root disappears under cover of 



Tuberculum olfactorium 



Olfactory tract 

 Optic tract | /' 

 Substantia perforata anterior | 

 tria olfactoria lateralis upon anterior | 



part of piriform area 

 fucleus amygdalae (cut surface) i 

 'iriform area (cut surface) j 

 iimen insulae ! 



Optic nerve 



Optic chiasma 



/ / Infundibulum 



Corpus mamillare 

 ( / Substantia perforata posterior 

 Oculomotor nerve 



Internal capsule 



)ptic radiation / / ; / 



Stria terminalis / / / 



Caudate nucleus / ; ,' 



Lateral geniculate body / / 



Brachium colliculi superioris [ 

 Thalamus (pulvinar) 



Medial geniculate body \ i 



Basis pedunculi cerebri \ 



Red nucleus 



Optic radiation 

 Caudate nucleus 



y Stria terminalis 

 Radiatio thalamo-temporalis (acoustic 

 radiation) passing from the medial 

 geniculate body into the anterior 

 transverse temporal gyrus 



Substantia nigra 



546. THE VENTRAL ASPECT OF PART OF THE PROSENCEPHALON, SHOWING THE EIGHT OPTIC TRACT. 

 The mesencephalon has been cut across. Olfactory area, dull yellow ; optic fibres, blue ; motor fibres, 

 red ; acoustic fibres, bright yellow. 



the medial geniculate body an<J a large proportion of its fibres arise or end in 



this nuclear body. The medial root, although it is composed of fibres which 



i intermingled with those of the optic tract, has nothing to do with the 



)tic nerve. These fibres, when traced forwards, cross the median plane in 



the posterior angle of the optic chiasma and are carried backwards alongside the 



opposite optic tract. The fibres constitute a bond of union, called the commissure 



of Gudden, between the medial geniculate body of one side and the colliculus inferior 



of the other (Fig. 547). 



The Optic Tract. The optic tract is composed of fibres which come (1) from 



3 lateral half of the retina of its own side ; and (2) from the medial half of the 



a of the opposite side, which have crossed the median plane in the optic 



chiasma. But in addition to the afferent retinal fibres there are a certain number 



