MOVEMENTS OF EYE. RANGE OF VISION. 179 



combination, in such a manner as to direct the pupil towards 

 all points of the circumference of the orbit. The straight, supe- 

 rior, inferior, external, and internal muscles move it upward, 

 downward, inward, and outward, and their successive action 

 gives it a movement of circumduction. The two oblique 

 muscles turn the eye on its antero-posterior axis, in such a 

 manner as always to maintain the horizontal position of its 

 transverse diameter, when the head or the body inclines to 

 the right or the left. All these muscles take a direct or indi- 

 rect part in every movement of the eye; if looking up or down, 

 for example, the straight, superior, or inferior acts alone ; the 

 other muscles assure the movement, and confine it to the 

 transverse axis. Such is the perfection of this mechanism, 

 that the cornea is raised or lowered without the least lateral 

 deviation, like the objective of a meridian glass; and the eye 

 perceives by this succession of movements if the image of a 

 line on the retina deviates o '00002 of an inch from the 

 vertical. 



The eyelids follow the movements of the globe when it is 

 raised or lowered, obeying the action of the muscles of which 

 they receive the aponeurotic prolongations. 



The movements of the two eyes are always symmetrical, 

 and of the same kind; both are raised or lowered at once, 

 directed to right or left, or around their axes; they can be 

 turned inwards simultaneously to see an object very near at 

 hand, or slightly outwards, when they turn from such a point 

 to one in the distance. Even when one eye is closed, the 

 globe turns in the same direction as that of the open eye. 

 This unity and variety of movement contribute to make the 

 eye the most important feature of the physiognomy. 



Extent and delicacy ' of vision. As regards the distance at 

 which man can distinguish objects, he is less gifted than 

 many other animals; but in every other respect his visual 

 powers are at least equal to that of inferior beings. We know 

 very little of the sensations produced in animals by colours; 

 it seems probable that they have a relative perception of 

 them to a certain extent, as the sight of red irritates the bull, 

 for example; and we know that birds of prey from a great 

 height in the air distinguish the colour as well as the form of 



