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
Muscle car Chrysler 300 is also recognized as one of the best-handling cars of its era. Studebaker entered the muscle car scene in 1956 with the Golden Hawk powered by a Packard V8 with . For the 1957 model year, the Rambler Rebel was the fastest stock American sedan according to "Motor Trend". "Musclecar Enthusiast" magazine describes this was "what some people believe to be the very first muscle car." the compact-sized (for the era) unibody 1957 Rebel might be "better known had AMC been successful in their attempt to offer it with Bendix fuel injection." The popularity and performance of muscle