DK KNOX on the Comparative Anatomy of the Eye. 71 



serted, that the base of the iris is fixed immediately into the ci- 

 liary muscle, but this is incorrect ; for, though it seems to be so 

 in some mammalia, yet in birds, and even in most of the mamma- 

 lia, we find a considerable space intervening betwixt the base of 

 the iris and the anterior edge of the ciliary muscle, which space 

 is filled up by a dark coloured loose cellular tissue. 



In the commencement of this Memoir, I have made a few 

 remarks on the Functions of the Iris, and, that I may not 

 seem to have overlooked the subject, I may observe, that many * 

 have ascribed muscular fibres to the iris, and, recently, Dr MAU- 

 NOIR has endeavoured to shew two sets of fibres, the one exter- 

 nal, radiated, the dilator of the pupil ; the other internal, nar- 

 rower, composed of circular fibres, the constrictor or sphincter 

 of the pupil. I have examined the iris very carefully in a great 

 variety of animals, but have never been able to detect any mus- 

 cular fibres as forming a part of its structure ; yet it is evi- 

 dently of a peculiar nature, and possesses in a high degree the 

 power of motion. It is most abundantly supplied with nerves 

 and bloodvessels, and, like other muscles, contracts under the 

 influence of galvanism f . 



* I have not been able to procure a copy of M. MAUNOIE'S little treatise on the 

 subject, so that I quote the passage from the " Traite D'Anatomie Descriptive," by 

 Dr CLOQUET. Neither have I been able to obtain a sight of some observations which 

 I find announced by the Journals, as having been made on the same subject by Dr 

 EDWARDS of Paris. I regret this the more, because, from the known accuracy of 

 that excellent physiologist, I feel well assured, that, on the points investigated by him, 

 he would leave little to be done by future observers. 



f Mr JOHN HCNTKE, whose physiological opinions scarcely admit of question, 

 seemed to think, a short time previous to his lamented death, that a fibrous structure 

 was not the sine qua non of muscularity. The application of this to the textures of 

 the iris and ciliary muscle is obvious. 



