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? to the League for £300. The book was extolled fulsomely by S.R. Thomas, of the NSW Department of Education, as follows; ""What Bird is That?" is the most comprehensive and informative bird book published in the Commonwealth – if not in the world. The coloured plates are a triumph not only of the genius and imagination of the artist – our own Neville Cayley on whom has fallen so fittingly the mantle of his famous father – but also of the block-maker’s and printer’s art. The publishers have done nothing finer of its kind. The life-like portrayals of our feathered