Iris sphincter muscle Iris sphincter muscle The iris sphincter muscle (pupillary sphincter, pupillary constrictor, circular muscle of iris, circular fibers) is a muscle in the part of the eye called the iris. It encircles the pupil of the iris, appropriate to its function as a constrictor of the pupil. It is found in vertebrates and some cephalopods. Initially, all the myocytes are of the smooth muscle type but, later in life, most cells are of the striated muscle type. Its dimensions are about 0.75 mm wide by 0.15 mm thick. In humans, it functions to constrict the pupil in bright light (pupillary light
What Bird is That? of "What Bird is That?" It was published in 1984 and incorporated all of Cayley’s paintings created over many years for his vision of releasing a “big bird book” and included a revised taxonomy. In the 53 years since its first edition, more than a hundred new bird species had been identified in Australia. Scientific names had been changed and groups of birds had been reordered. Lindsey brought "What Bird is That?" up-to-date with the latest birding conventions of the time, as well as contributing a valuable supplementary list of birds and a scholarly catalogue of Cayley’s paintings. The "Signature