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ami railial tibres. The fonnei' ciiciivlc the im|)il and are inserted in tlie visor- 

 like fuld of tlie iris. The latter arise fidni the margin of the sclerotic cnj) and 

 interweave with the circular tibres. The contraction of the circular fibres narrows 

 the pupil and draws the visor down into it. wdiile the contraction of the radial 

 fibres dilates the pupil and draws up the Nisor. The inner epithelium is contin- 

 uous at the inner edge of the iris with the outer epithelium and at its peri- 

 phery with the outer layer of the ciliary body. Its cells are cubical and are 

 filled with black pigment. 



The eyeball is held in ])lace by nine muscles and by a somewhat cylindrical 

 fascia which stretches from the equator- of the eye to the margins of the optic 

 cup of the skull and so , with the eye , encloses the optic ganglion and the wiiite 

 bodies. The inner side of this fascia is supported by the preorbital cartilage 

 which projects horn the pedal process of the skull forward and slightly down- 

 ward between the outer chamber and the eyeball. The nine orbital muscles, how- 

 ever, form the chief attachment of the eye. They lie in the orbital fascia and 

 are attached with it to the eyeball. The muscles arise from three points and so 

 naturally fall into three groups viz. 1) two that arise from the cerebral process 

 of the skull : i') three that arise from the lower part of the outei' edge of the 

 skull : and 8) four that arise from the pedal process and the preorbital bar. One 

 of the two arising from the cerebral process passes outward and downward to the 

 dorsal surface of the eye. The other passes downward between the muscles of 

 this third group and the eye , then outward to its lower surface. Of the three 

 that arise from the outer edge of the skull : one , a slender band , passes upward 

 and is inserted upon the upper part of the dorsal surface of the eye ; another , 

 a small short muscle, reaches directly forward to the lower part of the dorsal 

 surface of the eye: the third, a strong muscle, goes forward to the lower sur- 

 face of the eye. The four remaining muscles arise from the pedal process or 

 from the preorbital bar. One passes from the former outward and downward to 

 the lower surface of the eye. A second arises from the same process and is 

 inserted upon the lower edge of the preorbital cartilage. A third muscle, appar- 

 ently a continuation of the last, arises from the opposite edge of the cartilage 

 and from the pedal process near the base of the preorbital cartilage and is in- 

 serted upon the ventral surface of the eye. The remaining muscle is a peculiar 

 digastric muscle which extends from eye to eye passing through a pulley at the 

 ventral end of the pedal process. From this pulley which may be considered 

 the origin of the muscle a slender tendon passes outward and forward upon each 

 preorbital bar and then ends in a small triangular muscular belly that is attached 

 by a broad fascia to the ventral surface of the eye. It is not probable that this 



