LITERARY NOTICES. 

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Harris, Wilfred. Binocular and Stereoscopic Vision in Man and Other Verte- 

 Ijrates, with its Relation to the Decussation of the Optic Nerves, the Ocu- 

 lar Movements, and the Pupil Light Reflex. Brain, 1904, 27. 107-147. 



'Stereoscopic' vision differs from 'binocular' in that iu the former 

 the images of a given object fall simultaneously on homonymous sides 

 of the two retinae, while in the latter they may fall either homonymous- 

 ly or heteronymously. Now from examining experimentally the optic 

 chiasm in the toad, chameleon, pigeon, owl, and rabbit, and from the 

 reports of others on the cat, mouse and rat, the author concludes (p. 

 107) that "The decussation of the optic nerves at the chiasma is com- 

 plete in all fishes, amphibia, reptiles and birds, whether possessed of 

 binocular vision or not ;" and this notwithstanding that (p. in) "In 

 the lowest fishes, the cyclostoma, .... the optic nerves do not cross 

 the middle line, but each arises from the corresponding side of the fore- 

 brain, the nerves passing to the eyes without decussation." At most, 

 the author may be said to have shown that 'binocular' (but not stereo- 

 scopic) vision is not incompatible with total decussation at the chiasm. 

 He thinks probable that "the association of the visual impression re- 

 ceived by the two eyes t)f the same object is effected by the commissur- 

 al fibres of the corpus callosinii." True stereoscopic vision is suppos- 

 ed impossible unless the decussation is only partial, that is, unless the 

 optic fibres from homonymous sides of the retinae lead to the same 

 cortical centres. 



The macula lutea is probably not represented in both halves of 

 the brain as has sometimes been concluded from the fact that in most 

 cases of permanent hemianopia, the dividing line between the blind 

 and the seeing halves of the field is found to pass around the fixation 

 point, leaving it included in the seeing half of the field for each eye. 

 But this fact is probably due to a greater power of resisting disease 

 possessed by the macular fibres, since in cases of transient hemianopia 

 the dividing line between the seeing and the blind fields passes exact- 

 ly through the fixation point, and when recovery sets in it begins at the 

 macular region. The macular fibres do not bifurcate at the chiasm. 



Conjugate, lateral and vertical movements of the two eyes (but 

 not movements of convergence) are directly associated with semi- 

 decussation of the optic nerves at the chiasm. The more complete 



