Underwater orienteering is an underwater sport that uses recreational open circuit scuba diving equipment and consists of a set of individual and team events conducted in both sheltered and open water that test the competitors competency in underwater navigation. The competition is principally concerned with the effectiveness of navigation technique used by competitors to swim an underwater course following a route marked on a map prepared by the competition organisers, a compass and a counter meter to measure the distance covered; the sport was developed in the Soviet Union during the late 1950s and is played in Europe. It is known as La Orientación Subacuática in Spanish; the sport has been known as Technical Disciplines. Each competitor has the following recreational diving equipment - a diving mask, fins, a diving weighting system, an open circuit scuba set including diving cylinder filled with only breathing air of atmospheric origin and the following instruments - underwater compass and distance counting meter.

Each competitor must tow a buoy to identify his/her position underwater at all times when in the water. Competitors in the Monk Competition are permitted to use one buoy between a pair of competitors provided a buddy line is used. An exposure suit is required. Competitors are not permitted to use underwater search techniques and aids such as rope assisted searches or sonar, or use underwater communication devices; the equipment used in this sport has evolved since the sport's creation in order to improve competitor performance. Firstly, all of the scuba equipment and instruments are now mounted together in a housing to create a streamlined form that can be held in front of the competitor to reduce resistance whilst swimming underwater and with a bracket to locate the instruments in front of the competitor allowing use whilst swimming and navigating the event courses. Secondly, competitors use monofins. Competitors are permitted to use survey equipment such as a theodolite or a total station to check maps issued by the competition organisers with exception to the maps for the Monk Competition.

However, competitors are not permitted to check distances and directions by swimming or operating a boat on the course. The competition is held in natural water bodies such as freshwater lakes. Site selection criteria include a maximum current of 4 metres/minute, water depth no less than 3 metres, underwater visibility to be at least 1 metre and water quality is to be in accordance with World Health Organization requirements for bathing water. Competition sites are not permitted to be located in shipping lanes and areas intended for boating and swimming activity; the site when in use for competition is marked by buoys anchored 50m from the course. Four individual events and three team events are described in the International Rules; the M-Course is a ‘M’ shaped course of a total length of 590 metres consisting of a starting buoy, three rounding buoys and a finish line. Competitors are required to swim underwater around the rounding buoys in sequence and cross the finish line within the time limit of 15 minutes 20 seconds.

Competitors are ranked using a point scoring system for rounding the three buoys and for course accuracy at the finish line. The 5-Point Course is a course of a total length of 650 metres consisting of a starting buoy and five orienteering points of which the last is the finish, all laid out in an irregular shape. Competitors are required to swim underwater around the course in sequence and to confirm the discovery of each orienteering point ‘by pulling or spinning it’. Competitors are ranked using a point scoring system for each orienteering point found and for the speed of the swim around the course; the Star competition is a star-shaped course of a total length of 600 metres consisting of a starting buoy, five rounding buoys and five orienteering buoys of which the last is the finish. Competitors are required to swim underwater around the course in sequence and to confirm the discovery of each orienteering point ‘by pulling or spinning it’. Competitors are ranked using a point scoring system for rounding the five buoys, for each orienteering point found and for the speed of the swim around the course.

The Parallel Race is a single-elimination tournament where pairs of divers from a pool of competitors numbered at 32 race against each other over five rounds until one competitor is left un-eliminated and therefore is the winner. The course consists of a pair of two triangular-shaped courses of equal overall length and located next to each other; each course has a total length of 220m and consists of one start buoy, one rounding buoy, one orientation buoy and a finish line of three to four metres width. The Monk Competition is an event where a team of two competitors is required whilst underwater to plan and navigate from the start to the finish of the course via a number of orienteering points shown on a waterproof map provided at the start of the event within a maximum time of 18 minutes; the map contains details of the shore lines, boundary of the competition area, the exact position of start and the control points to be located. The course consists of one starting buoy and at least five control points of which the last to be located is the finish point.

All of the control points with exception to the finish point are not visible above the water's surface. The overall length is 650 metres with control points spaced at 100 to 150 me

The rectococcygeal muscles are two bands of smooth muscle tissue arising from the 2nd and 3rd coccygeal vertebrae, passing downward and forward to blend with the rectal longitudinal smooth muscle fibers on the posterior wall of the anal canal. The rectococcygeal muscles are composed of smooth muscle and run from the anterior surface of the 2nd and 3rd coccygeal vertebrae down the posterior wall of the rectum as a triangular shaped muscle before branching and inserting among the various muscles and fascial structures associated with the pelvic diaphragm and anal canal and collectively called longitudinal anal muscles. There are some differences in the retrococcygeal muscle architecture between females. In males the muscle inserts with the fascia of the levator ani to either side of the rectum or to other fascial elements of the pelvic diaphragm. In females the rectococcygeal muscle additionally runs around the sides of the rectum to connect to the rectovaginal fascia of the posterior vaginal wall.

There is evidence suggesting that the retrococcygeal muscles are ~2-fold thicker in females. The rectoccygeal muscles are innervated by autonomic nerves associated with the inferior hypogastric plexus; the rectococcygeal muscles form part of the complex arrangement of muscle surrounding the rectum, sometimes termed the anal-sphincter complex, which act to stabilise and support the anal canal during defecation. The rectococcygeal muscle acts to lift the sphincter, thereby shortening the rectum and aiding evacuation. In many animals with tails, such as horses and dogs, the rectococcygeal muscles are involved in the response to the raising of the tail during defecation. In tailed animals the muscle attaches to vertebrae in a more caudal position than in humans due to the additional vertebrae in the tail, in dogs there are connections to the 5th and 6th caudal vertebrae and in horses to the 4th or 5th; the rectococcygeal muscle in the rabbit is notable for being one of the fastest contracting mammalian smooth muscles known.

Rectococcygeus muscle at Systematized Nomenclature of Medicine - Clinical Terms This article incorporates text in the public domain from page 1186 of the 20th edition of Gray's Anatomy