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The foremost muscle was described by Sir E,. Crampton, 

 and bears his name. Behind, it is always attached to the 

 sclera, and in front to the cornea, either directly or to a 

 tendinous prolongation of the inner corneal lamellae. Shorten- 

 ing of this muscle would therefore tend to bring them closer 

 together, and as the sclerotic with its strong bony ring is the 

 least mobile of the two, the muscle would tend to retract or 

 depress the cornea, and to counteract any force operating 

 simultaneously in an opposite direction to increase its con- 

 vexity. The posterior muscle always passes between the 

 sclera and choroid. Separated by a wide interval from 

 Crampton's muscle in eagles, as I have already said, in many 

 smaller birds it apj^ears on a cursory examination to be a 

 continuation of the posterior bundles of this ; yet a careful 

 scrutiny always shows that it has distinct attachments. In 

 many birds there is an accessory slip attached anteriorly to 

 a prolongation of the same tendinous band from the cornea 

 into which the inner ends of the bundles of Crampton's 

 muscle are inserted, and in some birds this muscular slip 

 exceeds that which stretches from the sclerotic to the choroid. 

 The contraction of either or both these muscular slips would 

 tend to draw the choroid forwards upon the sclerotic and 

 tighten it on its contents. They are tensors of the choroid 

 and the homologues of the human ciliary muscle. The 

 pecten, which, before the ciliary muscles were known, was 

 ever regarded as the agent of accommodation, is not any 

 longer considered so. 



Reptiles have an iris very like that of birds. The primitive 

 muscular fibres, of the striped kind, are extremely fine ; they 

 also exhibit divisions and a plexiform arrangement. They 

 are also disposed in two sets, one circular, the other radiating, 

 differing from those of birds mainly in their less develop- 

 ment. 



Crampton's muscle I have not yet found in reptilian eyes, 

 but all which I have examined, embracing several chelonia 

 and many lizards and snakes, have a striped tensor muscle 

 of the choroid passing from the sclerotic to this coat, occu- 

 pying the same posterior position as its homologue in the 

 bird, and corresponding functionally to the human ciliary 

 muscle. 



I have hitherto been baffled in every endeavour to decipher 

 the details of the muscular part of the accommodative appa- 

 ratus in batrachia. In the frog's eye, the quantity and the 

 blackness of the pigment offer great difficulties. An un- 

 striped sphincter papillae is generally demonstrable. It is 

 composed of long spindle-cells enclosing an elongated 



