1224 



HUMAN ANATOMY. 



The entire commissure, however, is not composed of optic fibres, since its posterior part 

 is formed by a bundle, known as Gudden's commissure (commissura inferior) (page mo), which 

 passes forward along the mesial side of the optic tract, loops around the posterior angle of the 

 commissure and enters the opposite tract. These fibres have no connection with the path of 

 sight-impulses, but are probably chiefly related with the median or internal geniculate bodies 

 and the inferior corpora quadrigemina (page mo). 



The optic commissure also contains fibre- strands that arch around its posterior angle, par- 

 allel with, but separated by a thin layer of gray matter from Gudden's tract. Concerning the 

 origin and destination of these fibres, termed Meynert's commissure (commissura superior), little 

 is known. By some they are regarded as continuations of the mesial fillet that, after decussa- 



FiG. 1050. 



Diagram showing course of retinal fibres in optic pathway and iheir connection with basal ganglia and primary 

 cortical centres ; smaller figure illustrates path of light-ray and resulting impulse through retina ; Ji, retina : ON, OC, 

 OT, OR, optic nerve, chiasm, tract and radiation , /*, pulvinar ; Eg, SQ, lateral geniculate and superior quadrigem- 

 inal bodies; Oc Cx, occipital cortex; ///, ly, IV, nuclei of eye-muscle nerves. 



tlon, pass to the globus pallidus of the lenticular nucleus of the opposite side. Others deny 

 such relations, while Kolliker describes them as bending upward, traversing the ventral part 

 of the cerebral peduncle, to end within the corpus subthalamicum (page 11 28). 



Additional commissural fibres (commissura ansata) descend from the floor of the third 

 ventricle and from the peduncle of the septum lucidum, by way of the lamina terminalis, to the 

 front and upper part of the optic chiasm ; other fibres pass from the ventricular floor to the back 

 of the chiasm. For the most part these fibres cross to the opposite side to be lost in the sub- 

 stance of the optic commissure. Although regarded as in away constituting a ventral optic 

 root, their connections and significance are not understood. 



The optic tract (Fig. 993) is the continuation of the optic nerve, its chief 

 constituents being the crossed and uncrossed retinal and the supplementary fibres. 

 On leaving the commissure, the tract diverges in front of the interpeduncular space, 

 mesial to the anterior perforated space and the termination of the internal carotid 

 artery, and sweeps outward and backward from the base of the brain around and 

 close to the cerebral peduncle, becoming flatter and broader as it proceeds. Near 



