Zoological Collections. 153 



anatomy makes us acquainted with, so far from illustrating the 

 mode in which sight is accomplished in man, would rather lead 

 us to believe that vision is variously modified in different ani- 

 mals, wherever a different structure is provided by nature. Nor 

 does the crossing without any union of the optic nerves in fishes 

 and some lizards militate against this general conclusion. It is 

 evident, from the position of the eyes of such fishes as are al- 

 luded to by Dr Wollaston, that they cannot see the same ob- 

 ject with both eyes at one time. 



The eyes are not the only organs of sense which, being 

 double, do communicate a single impression to the sensorium. 

 We have a parallel instance in the sense of hearing. The fact 

 is, that we have no proof that there is any more correspond- 

 ence between the pictures in the eye, and the sensations pro- 

 duced by them in the brain, than there is resemblance between 

 the sounds of any given words of a language and the senti- 

 ments excited thereby in the sensorium. Nor does it appear 

 necessary towards unity of perception of any given object, that 

 the impression on the organs of sense should be single. Brown 

 has observed, in his Philosophy of the Human Mind, that the 

 two words he conquered, produced in the mind the same single 

 idea or impression as the word vicit. 



I think the aggregate of the foregoing paper will be admit- 

 ted as sufficient proof that there is no decussation of the optic 

 nerves on the sella turcica in man. If we wish to ascertain 

 how single vision is accomplished with two eyes, we must seek 

 other reasons for that phenomenon than those which have been 

 assumed by Sir Isaac Newton and by Dr Wollaston. The 

 facts above stated appear to me so demonstrative on this sub- 

 ject, that I am satisfied those authors, with such evidence, 

 would not have adopted the conclusions they have published. 



Art. XXV.— ZOOLOGICAL COLLECTIONS. 



1. Account of one of the Brood of Boa Constrictors.* In a Letter from 

 David Scott, Esq. to George Swtnton, Esq. 



One of the young boas having died, I send him down to you in spirits. 

 He was two years and two months old, during which time he increased in 

 • See this Journal, No. viii. p. 221, and No. xiii. p. 164. 



