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A TEXTBOOK OF PHYSIOLOGY 



the alteration of the lens corresponding to the change of accommo- 

 dation, the images from the anterior surface of the lens are seen to 

 vary, as described above. 



The Mechanism of Accommodation. According to the received 

 hypothesis, the meridional and radial fibres of the ciliary muscle 



PIG. 344. DIAGRAM TO SHOW HOW ANTERIOR SURFACE OF THE LENS BECOMES MOKE 

 CONVEX DURING ACCOMMODATION FOR NEAR VISION. 



contract and pull forward the posterior part of the ciliary body 

 and the anterior part of the choroid, with the hyaloid membrane. 

 This slackens the suspensory ligament and diminishes its pull upon 

 the capsule of the lens, and the lens then, by its own elasticity, is free 

 to assume a more convex shape. It is further suggested that the 



FIG. 345. To ILLUSTRATE THE MOVEMENT OF THE CORNEO-!RIDIC ANGLE IN 

 ACCOMMODATION. (Thomson Henderson.) 



The ciliary sphincter moves from c to c', the cribriform ligament is pulled taut, 

 affording ready passage of aqueous into the suprachoroidal space. The angle 

 of the anterior chamber is not deepened in an anatomical sense. 



circular fibres of the ciliary muscle, by their contraction, squeeze the 

 free edges of the lens in a sphincter-like manner, thereby helping to 

 squeeze the anterior surface forwards. The circular fibres are especi- 

 ally well developed in long-sighted people, who accommodate with 

 special effort. It is said that the lens becomes more movable in the 

 accommodated eye, as it can then be made to shake by sudden 

 movements of the head. The essential part of the act of accommo- 



