408 THE BALL OF THE EYE. 



contact with the ball of the eye. Dr. Physick has suggested, 

 that it will also keep the edges of the eyelids applied to the 

 eyeball in cases of extreme emaciation where the eye is 

 much sunk. While investigating this subject, rny attention 

 was called by Dr. Harlan to a motion prevailing in the puncta 

 lachrymalia, with which I was before unacquainted. The 

 puncta project themselves an/1 retract much after the manner of 

 an earth worm, and it is probable that the latter motion may be 

 produced in some measure by this muscle. 



In consideration of some of the functions of this muscle, I 

 have ventured to propose that it be called Tensor Tarsi.]* 



The tendons of the four recti muscles, being spread upon the 

 anterior part of the ball of the eye, constitute a partial covering, 

 which has been called Tunica Albuginea.^ This tendinous 

 expansion does not extend to the edge of the cornea, but stops 

 short of it by several lines.J 



Of the Ball of the Eye. 



The spherical figure of the eyeball depends upon a strong 

 and firm external coat called the Sclerotica ; which has an 

 aperture in its anterior part, filled up with a transparent sub- 

 stance denominated Cornea, that closes it perfectly. 



The antero-posterior diameter of the globe of the eye, is 

 greater than the transverse. The former is about ten or twelve 

 lines, the latter about one line less. This difference is owing 

 to the projection of the cornea, it being a section of a lesser 

 sphere. A Transverse vertical section of the globe, taken at 

 any part, will represent a perfect circle. In short-sighted 

 persons, the antero-posterior diameter of the eye is greater 

 still, relatively to the transverse. A similar difference exists 



* For a more full account of this muscle, see Homer's Anatomy. 



f This is no longer considered as a proper membrane ; it is inseparably con- 

 nected with and forms a part of the sclerotic coat. The partial expansion of 

 these tendons seen through the conjunctiva, gives a brilliant glistening appear- 

 ance to the eye, from which is derived 4he common term, white of the eye. p. 



:ji By line, is meant one-twelfth of an inch. 



