138 



Accordingly, it appears, that in those animals where the partial 

 decussation of the optic nerves exists, making the sensations of each 

 eye dependent on both optic lobes, (viz. in all the mammalia and 

 birds,) the decussation at the pyramids also exists, according to the 

 observations of Cuvier, Serres, and others ; and the sensation and 

 motion of either side of the body appear from the experiments of 

 Flourens and others, as well as from observations of the effects of 

 injury or disease, to be dependent on the other side of the brain ; 

 whereas in reptiles and fishes, where there is no commissure of the 

 optic nerves, and one optic lobe only is concerned in the vision oi 

 one eye, there is no decussation at the pyramids, and no crossing ef- 

 fect of injury of the brain, to the opposite side of the body, has been 

 observed. 



If this speculation be well founded (and it is admitted that far- 

 ther anatomical inquiries are requisite to justify a decided opinion 

 upon it), the peculiar course and mode of implantation of the optic 

 nerves, in most if not all animals, and the partial decussation of the 

 optic nerves, and the decussation at the pyramids in the two higher 

 classes, are all parts of the arrangement by which Nature brings the 

 intimations given by the sense of Sight, which are of course partly 

 regulated by the laws of light, into harmony with those given by 

 the sense of Touch, which have no connexion with these laws ; and 

 enables those animals that use both eyes at once, to derive correct 

 information as to the number and position of objects from the sen- 

 sations simultaneously excited in both, notwithstanding that the 

 images which are essential to these sensations are double, inverted, 

 and reverted. 



Mondaij, 18th April 1886. 

 Sir T. M. BRISBANE, Bart. President, in the Cliair. 

 The following gentlemen were duly elected ordinary Fellows 

 of the Society : 



1. Martin Barry, M. D. 



2. Robert Steuart, Esq- M. P. 



The following donations were presented : 

 Nouveaux Memoires de I'Academie Royale des Sciences et Belles 



Lettres de Bruxelles. Tome ix. 

 Memoires couronnes par I'Academie Royale des Sciences et Belles 



Lettres de Bruxelles. Tome x. 



