VISION, 4 4<) 



interfered with its use by obstructing the trans- 

 mission of light. 



The eyes of quadrupeds agree in their general 

 structure with those of man. In almost all the 

 inferior tribes they are placed laterally in the head ; 

 each having independent fields of vision, and the 

 two together commanding an extensive portion of 

 the whole sphere. This is the case very generally 

 among Fishes, Reptiles, arid Birds. Some excep- 

 tions, indeed, occur in particular tribes of the first 

 of these classes, as in the Uranoscopns, where the 

 eyes are directed immediately upwards; in the 

 Ray and the CaUionymus, where their direction is 

 oblique ; and in the Pleuronectes, where there is a 

 remarkable want of symmetry between the right 

 and left sides of the body, and where both eyes, as 

 well as the mouth, are apparently situated on one 

 side. Among birds, it is only in the tribe of Owls, 

 which are nocturnal and predaceous, that we find 

 both eyes placed in front of the head. In the lower 

 quadrupeds, the eyes are situated laterally, so that 

 the optic axes form a very obtuse angle with each 

 other. As we ascend towards the Quadrumana we 

 find this angle becoming smaller ; till at length the 

 approximation of the fields of view of the two eyes 

 is such as to admit of their being both directed to 

 the same object at the same time. In the human 

 species the axes of the two orbits approach nearer 

 to parallelism than in any of the other mammalia ; 

 and the fields of vision of both eyes coincide nearly 

 in their whole extent. This is probably a cir- 

 cumstance of considerable importance with regard 

 to our acquisition of correct perceptions by this 

 sense. 



VOL. II. G G % 



