548 STUDIES IN ADVANCED PHYSIOLOGY. 



compression, and so continually flattened. The relation of 

 this fact to the power of accommodation will be evident a 

 little further on. 



That part of the hyaloid membrane which immediately 

 surrounds the lens is called the capsule of the lens, while 

 that next to the capsule of the lens is spoken of as the sus- 

 pensory ligament. 



8. Ciliary Muscles and the Muscles of Accommodation. 

 There occur in the iris two sets of muscles ; a circular set 

 by the contraction of which the pupil is made smaller, and 

 a radial set, the contraction of which causes an increase in 

 the opening of the pupil. In addition to these muscles of 

 the iris there are found imbedded in the choroid coat just at 

 the point where the choroid coat and the cornea meet, a 

 system of muscles known as the muscles of accommoda- 

 tion. These muscles are attached firmly at one end where 

 the cornea and the choroid unite, from which point they ex- 

 tend backwards through the choroid in such a way that when 

 they contract they pull the choroid coat forward towards the 

 cornea. It will be pointed out that by means of these mus- 

 cles the eye is focussed for far and near. At the point 

 where the cornea and the iris meet there is a small canal 

 running around the eye, called the canal of Schlemm. Be- 

 tween the two layers of the hyaloid membrane where they 

 separate to enclose the lens there is a second canal en- 

 circling the lens called the canal of Petit. Between the 

 suspensory ligament and the iris there is usually a small 

 space which is but a continuation of the space containing 

 the aqueous humor. This space is called the posterior 

 chamber of the aqueous humor. 



Reference to the diagram of the eyeball will show its 

 close analogy to a camera, in which the refracting media 

 are the cornea, the lens and the humors. The image will 

 fall on the retina, and as the light usually enters the eye in 

 a certain straight direction the image will regularly fall 

 straight behind the lens. This point on the retina where 

 the most acute vision occurs is called the yclloiv spot. It 



