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 designed 2009 Camaro, which bears some resemblance to the 1969 model. The blend between old and new has fueled the muscle car revival. The mid-1960s muscle car era came to define what baby-boom men would expect from their automobiles. While the aging baby boom generation inspired the modern demand for classic-type American Muscle cars, the consumer market is much more diverse than it was in the 1960s and 1970s. Looking at modern muscle as a social trend, Ford and GM are the "innovators," followed by baby boom males in their 50s as "early adopters." The big bulge or "early majority"