220 The Ciliary Muscle and LE, 
increased by a ring of bony plates, and behind those by a cartila- 
ginous lamina intercalated in the fibrous sclera. The aliary pro- 
cesses 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 those in the ciliary region. 
In the iris the muscular 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 lies the stratum of circular fibres, forming a contimuous sheet 
from the pupil to the attached border of the iris, stouter here and 
at the pupil, and thinner intermediately. They are easily demon- 
strated 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 which 
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. These circular muscular bundles which bound the pupil are 
manifestly a constriction of sphincter pupill, but the bundles at the 
outer border of the iris in contracting not improbably compress 
the corresponding front of the lens, and so tend to increase the con- 
vexity of the uncovered part of the front of the lens in the pupillary 
area, as H. Miller has suggested. This view of their action derives 
support from the beautiful points of those bundles which we often 
find on the lens after death. 
The primitive muscular fibres of the iris are much finer than 
those of the voluntary muscles of the limbs, from which they differ 
also in dividing and combining in nets. 
The ciliary region contains two muscles. In the largest rap- 
torial birds these are quite distinct, they are separated by a consi- 
derable interval; but in the eyes of smaller birds these muscles are 
approximated, and in these their distinctness is less obvious, yet, I 
think, none the less real. 
The foremost muscle was described by Sir P. Crampton, and it 
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 lamelle. Shortening of this muscle would there- 
fore tend to bring these attachments together, and as the sclerotic 
with its bony ring is the least mobile of the two, the muscle would 
tend to retract or depress the cornea, and so counteract any force 
simultaneously operating in an opposite direction to increase its 
convexity. 
The posterior muscle always passes between sclera and choroid. 
