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1. any annular or circular organ, structure, or area.
2. in chemistry, a collection of atoms united in a continuous or closed chain.
abdominal ring, external an opening in the aponeurosis of the external oblique muscle for the spermatic cord or round ligament.
abdominal ring, internal an aperture in the transverse fascia for the spermatic cord or round ligament.
Albl's ring a ring-shaped shadow in radiographs of the skull, caused by aneurysm of a cerebral artery.
Bandl's ring see bandl's ring.
benzene ring the hexagon representing the arrangement of carbon atoms in a molecule of benzene, different compounds being derived by replacement of the hydrogen atoms by different elements or compounds.
Cannon's ring a focal contraction seen radiographically at the mid-third of the transverse colon, marking an area of overlap between the superior and inferior nerve plexuses.
conjunctival ring a ring at the junction of the conjunctiva and cornea.
constriction ring 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.
fibrous ring of heart anulus fibrosus.
halo ring a metal orthosis used for traction in the treatment of spinal cord injuries. The halo apparatus can maintain stability and alignment of the cervical vertebrae while the patient is out of bed.
inguinal ring, deep an aperture in the transverse fascia for the spermatic cord or the round ligament.
inguinal ring, external superficial inguinal ring.
inguinal ring, internal deep inguinal ring.
inguinal ring, superficial an opening in the aponeurosis of the external oblique muscle for the spermatic cord or the round ligament.
Kayser-Fleischer ring a golden brown or green discoloration in the zone of Descemet's membrane in the limbic region of the cornea seen in wilson's disease and other liver disorders.
pathologic retraction ring 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 infant. See also bandl's ring.
physiologic retraction ring the demarcation between the upper, contracting portion of the uterus in labor and the lower, dilating part.
Schwalbe's ring a circular ridge composed of collagenous fibers surrounding the outer margin of Descemet's membrane.
tympanic ring the bony ring forming part of the temporal bone at birth and developing into the tympanic plate.
umbilical ring the orifice in the abdominal wall of the fetus for transmission of the umbilical vein and arteries.
vascular ring a congenital anomaly of the aortic arch and its tributaries, the vessels forming a ring about the trachea and esophagus and causing varying degrees of compression.
in the fetus, a more or less complete bony ring at the medial end of the cartilaginous external acoustic meatus, to which is attached the tympanic membrane.