424 Mr. A. T. Norton on the Accommodation of Vision. [June 19, 



and as the insertion 5 to 5 the fibres into the connective tissue of the 

 choroid coat of the eyeball, and the remaining fibres into the connective 

 tissue of the erectile mass and ciliary processes. 



Judging the action of the muscle from the attachment of its fibres, he 

 states that those fibres inserting into the choroidea, and which are seen 

 to pass around the veins derived from tissues which he terms erectile, 

 must, when contracting, compress those veins, and so cause the erection 

 of the ciliary processes and ciliary mass 5 whilst the fibres of the muscle 

 which curve round to insert into the connective tissue of the ciliary pro- 

 cesses, when contracting, cause those structures to approach the muscle, 

 thereby tensing them upon their contained vessels, so as to render them 

 solid and to prevent them from flattening upon the anterior surface of 

 the lens. 



The attachment of the ciliary muscle to the suspensory ligament of 

 the lens, either primarily or secondarily, is denied ; so that the con- 

 traction of that muscle cannot draw forward the suspensory ligament as 

 hitherto described. 



The existence of a ciliary ligament is not admitted. 



The author continues : — 



Accommodation is known to depend upon the convexity of the lens. 



The convexity of the lens depends upon the size of the erectile organs 

 (ciliary processes and ciliary mass), which, when the eye is accommodated 

 for closest vision, assume the greatest amount of erection. These erec- 

 tile organs form a circular cushion, which overlaps . the equator of the 

 lens ; and as the size of this cushion increases as the erectile tissue 

 becomes filled with blood, so does the cushion exert a greater amount of 

 pressure upon the equator of the lens, decreasing the substance of the 

 lens at its equator, and increasing it at its poles ; in this manner the lens 

 is increased in convexity and accommodated for near vision. 



So far accommodation may be effected without the aid of an iris ; but 

 without an iris the change of accommodation from- extreme distant to 

 extreme near vision must occupy the time required to fill the ciliary 

 processes with blood to complete erection. With the iris the change is 

 almost (but not quite) instantaneous. 



Jrom the circumferential attachment the iris curtain passes obliquely 

 forward for ^ to ^\ inch, and then falls at a sharp angle. [In opera- 

 tions the iris tears from this angle, and not from its circumferential 

 attachment.] The plane cf the iris is therefore ^ to inch in front of 

 its attachment. 



Papillary narrowing is associated with accommodation for near vision. 

 The muscular fibres of the iris are circular, and radiating ; and though 

 the two sets would appear to counteract each other, yet both can act at 

 the same time. When the circular fibres (sphincter) contract, the 

 radiating fibres contract with a power not sufficient to overcome the 

 contraction of the circular fibres, but with a power sufficient to tense the 



