1. any annular or circular organ, structure or area.
2. in chemistry, a collection of atoms united in a continuous or closed chain.
- abdominal r. (external) — an opening in the aponeurosis of the external oblique muscle for the spermatic cord or round ligament. Called also external inguinal ring.
- abdominal r. (internal) — an aperture in the transverse fascia for the spermatic cord or round ligament. Called also internal inguinal ring.
- Bandl's r. — see bandl's rings.
- r. cell — an immature granulocyte, intermediate between the myelocyte and metamyelocyte, found in the bone marrow of rats. There is a ‘hole’ in the nucleus.
- ciliary r. — the posterior part of the ciliary body of the eye, a continuation of the choroid.
- conjunctival r. — a ring at the junction of the conjunctiva and cornea.
- constriction r. — a contracted area of the uterus, where the resistance of the uterine contents is slight, as over a depression in the contour of the fetus, or below the presenting part.
- deep inguinal r. — an aperture in the transverse fascia for the spermatic cord or the round ligament.
- docking r. — see elastrator.
- femoral r. — the abdominal opening of the femoral canal through which the femoral nerve and blood vessels pass from the peritoneal cavity to the limb.
- inguinal r. — see abdominal ring (above).
- pancreatic r. — the ring in the pancreas that accommodates the portal vein.
- r. precipitin test — see precipitin reaction.
- preputial r. — the rim of the external orifice of the prepuce proper, the internal prepuce, on the penis of the horse.
- retraction r. — the demarcation between the upper, contracting portion of the uterus in normal parturition and the lower, dilating part.
- retraction r. (pathological) — a complication of prolonged labor marked by failure of relaxation of the circular fibers at the internal opening of the cervix, obstructing delivery of the fetus.
- Schwalbe's r. — see
schwalbe's ring. - scleral r. — see ring of ossicles.
- stallion r. — a rubber ring fitted over the glans penis of the stallion which discourages erection and masturbation.
- superficial inguinal r. — a fissure-like opening in the aponeurosis of the external abdominal oblique muscle for the spermatic cord or the round ligament.
- r. test — see ascoli test.
- tympanic r. — the bony ring forming part of the temporal bone at birth and developing into the tympanic plate.
- umbilical r. — the orifice in the abdominal wall of the fetus for transmission of the umbilical vein and arteries.
- r. vaccination — vaccination of all animals in a zone around an area in which the subject disease occurs. A preventive strategy that contains the infected population so that the eradication team has a finite target.
- vascular r. — any of a number of congenital anomalies of the aortic arch and its branches, the vessels forming a ring about the trachea and esophagus that cause varying degrees of compression, vomiting and esophageal dilatation. See also persistent right aortic arch.
