170 SENSORIAL FUNCTIONS. 



the eye forward, serving as antagonists to the straignt 

 muscles. The upper oblique muscle, s, is very remarka- 

 ble for its anatomical structure. Its tendon passes through 

 a little aperture in a piece of cartilage, which is fast- 

 ened to the upper margin of the orbit. The tendon then 

 turns back, forming a complete pulley, and is inserted 

 into the upper side of the eye-ball as seen in the figure. 

 It is obvious that the effect produced by the contraction 

 of this muscle, is exactly contrary to that of the action 

 of its fibres. 



513. This muscle affords another instance of that sim- 

 plicity, effect, and design, which we so often meet with in 

 the study of nature, and especially in the mechanism of 

 the human frame. Taking the contiguous parts as they 

 are, in no other situation could this muscle have been 

 placed, without interfering with the action of some other 

 part, nor could any other construction occupying the same 

 limited space, have been devised to answer the same pur- 

 pose, being made to pull in a direction contrary to its own 

 action. 





MAGNITUDES AND DISTANCES OF OBJECTS. 



514. An inquiry into the philosophy of vision for the 

 purpose of ascertaining in what manner we are able to 

 appreciate the distance of an object by its apparent mag- 

 nitude, together with the subject of perspective, and the 

 phenomena of vision generally, would lead us far beyond 

 the limits of this work. We will, however, cite two or 

 three curious cases, in order to show how far we are able 

 to gain a knowledge of the -forms, magnitudes, and dis- 

 tances of things without the aid of the eyes. So far as 

 any of us can remember, we have always been able -to 

 form a judgment of the forms, distances, and magnitudes 

 of objects, by the eye, and especially with respect to 

 those which are not at very remote distances. But 



w far these distances are appreciated by walking from 



VJi 



the 

 ho 



Describe the upper oblique muscle of the eye, and show its use. What 

 is said of the mechanism of these 



