596 SIGHT. 



denied the existence of an optic nerve in this animal.* In the zemni, or blind 

 rat, the integuments, overspread with hair and of uniform thickness, cover the 

 whole side of the head, and under it a black spot only is found, a mere rudiment 

 and useless. In these cases, the sense of hearing is extremely acute ; and both it 

 and other senses in the bat, which has very small eyes, though a nocturnal animal. 

 For those which prey by night, as well as those which have to see at a distance in 

 order to pursue or avoid pursuit, as the carnivora, rodentia, and ruminantia, have 

 large eyes. The pupil is transverse in many ruminants whose head inclines down- 

 wards, so that they can see extensively to the side and backwards when feeding : 

 while in those which spring from a height, or climb, it is frequently perpen- 

 dicular, so that their vision is extensive upwards and downwards. In almost 

 all the inferior tribes, just as is generally the case in fishes, reptiles, and birds, they 

 are placed laterally in the head, with two independent fields of vision, the optic 

 axes forming a very obtuse angle together, so as to give a very large view. As 

 we ascend towards the quadrumana, the optic axes form a smaller angle, the 

 two fields of vision approach, so that both eyes can be directed simultaneously 

 to the same object ; and the same is noticed in nocturnal quadrupeds, and in 

 owls ; and in us the axes are more nearly parallel than in any other mam- 

 malia, the fields of vision coincide in almost all their extent, and precision of 

 visual impressions is thus augmented. In carnivorous quadrupeds, the back 



* Not only did Dr. Magendie deny this, but M. Serres, doing the same thing, 

 declared that the mole and several others saw by means of other nerves than the 

 optic, and thus argued that one part of the nervous system could perform the 

 functions of another. " The sense of smell," says he, " can be transported from one 

 nerve to another, according to the ingenious remark of Professor Dumeril. From 

 the observations of Scarpa, Cuvier, Jacobson, and Treveranus, hearing may be 

 partly performed by the fifth pair. From my researches on the mole, chryso- 

 chlore, shrew mouse, zemni, proteus, &c., these animals see by some other nerve 

 than the optic. Is it not such facts as these that gave M. Cuvier the idea of the 

 general law which he has stated, of the difference of the functions of nerves 

 depending rather upon the different organisation of the parts to which they are 

 distributed, than upon their own nature." Gall observes that M. Serres 

 must have forgotten the remark in his treatise on the difference of nerves (MON 

 traite sur la difference des nerfs, in his 4to work, t. i. p. 127.), that Cuvier dis- 

 avowed this idea in his Comparative Anatomy, p. 492., where he says, "analogous 

 parts constantly receive their nerves from the same pair in all animals, whatever 

 be the situation of the parts, however circuitous the course which the nerve has 

 to take. Analogous nerves have always a similar distribution : always go to 

 the same parts. Even those small pairs whose distribution is the most limited, 

 and which might easily be supplied by others, as the fourth and sixth, preserve 

 their existence and office." Gall then states that he has examined the mole and 

 found an optic nerve, though extremely small ; and adds that M. Baily has 

 confirmed his observations, and demonstrated the nerve to St. Hilaire and Cuvier. 

 Naturalists now agree with Gall. (Gall, 1. c. 8vo. t. vi. p. 307. sqq.) 



