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
Clay-colored sparrow Clay-colored sparrow The clay-colored sparrow or clay-coloured sparrow ("Spizella pallida") is a small sparrow of North America. Adults have light brown upperparts and pale underparts, with darker streaks on the back. They have a pale crown stripe on a dark brown crown, a white line over the eyes, a dark line through the eyes, a light brown cheek patch and brown wings with wing bars. The short bill is pale with a dark tip and the back of the neck is grey; they have a long tail. Non-breeding adults and immature resemble chipping sparrows and Brewer's sparrows; they often form