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The capsule and its epithelium, and the lens-fibre are essen- 

 tially like those of man. The ciliary processes are simple, 

 the suspensory ligament and its connections, the arrangement 

 of the ciliary muscle and kind of muscular tissue are such as 

 we find them in the human eye. Birds, however, present 

 very striking differences. In a bird's eye, we are immediately 

 struck with the great extent of the ciliary region compared with 

 that occupied by the retina. It is the stoutest part of the outer- 

 most case of the eyeball ; its strength is increased by a ring of 

 bony plates, and behind these by a cartilaginous lamina inter- 

 calated in the fibrous sclera. The ciliary processes are fringed 

 and papillose, not simple, and a plaited membrane, the pecten, 

 projects like a wedge into the vitreous humour from the 

 entrance of the optic nerve. 



All the intraocular muscles are composed of striped fibre, 

 the iris as well as tbose in the ciliary region. 



In the iris the miiscular fibres are disposed in two sets, one 

 having a radial direction, the other circularly disposed. The 

 radial fibres pass between the great circumference of the iris 

 and the pupil, coursing along the back of the iris just in front 

 of the uveal epithelium. These are the dilators of the pupil. 

 In front of them there is a stratum of circular fibres forming 

 a continuous sheet from the pupil to the attached border of 

 the iris, stouter here and at the pupil, and thinner interme- 

 diately. They are easily demonstrated in the iris of any large 

 bird by dissecting off the thick layer of pigmented connective 

 tissue which forms the front of the iris, and which is, in great 

 part, a derivative of the ligamentous tissue that fixes the 

 border of the iris to the margin of the anterior chamber. It 

 is in this connective tissue that the great blood-vessels and 

 nerves lie. Those circular muscular bundles which bound 

 the pupil are manifestly a constrictor or sphincter pupillse ; 

 but the bundles at the outer border of the iris in contracting 

 not improbably compress the corresponding part of the lens, 

 and so tend to increase the convexity of the uncovered part 

 of the lens in the pupillary area, as H. Miiller suggested. 

 This view of their action derives support from the beautiful 

 prints of these bundles which are often found on the lens in 

 dissection. 



The primitive muscular fibres of the iris are much finer 

 than those of the voluntary muscles of the limbs, from which 

 they also differ in dividing and combining in nets. 



The ciliary region contains two muscles. In the largest 

 raptorial birds these are quite distinct ; they are sepaiated by 

 a considerable interval ; but in the eyes of smaller birds the 

 muscles are approximated, and in these their distinctness is 

 less obvious, yet, 1 think, none the less real. 



