A swimming squid takes up and expels water by contracting radial and circular muscles in its boneless mantle wall. (scientificamerican.com)
Psoas is a thick circular muscle that runs along the front of the spine, attaching along lumbar vertebrae 1 - 5 and inserting into the top of the femur. (physiologicnyc.com)
Caffeine relaxes the lower esophageal sphincter, a circular muscle that creates a valve between the esophagus and the stomach. (health.com)