The normal diameter of the mitral annulus is , and the circumference is . Its thick periphery forms a fibrocartilaginous ring called the annulus tympanicus or Gerlach's ligament. It travels through it lateral to the frontal nerve outside the annulus of Zinn. Baroclinic instability can be investigated in the laboratory using a rotating, fluid filled annulus. The liquid is placed within the annulus of one cylinder inside another. A shaftless flywheel eliminates the annulus holes, shaft or hub. This allows measurement of the leaflet thickness and their displacement relative to the annulus. Once at the surface, the gas is collected through piping connected to the annulus. The case had red lacquer sealant around the primer annulus. This determines the shear rate inside the annulus. The series converges uniformly on compact subsets of the interior of the annulus of convergence. Excess load is transferred to the "annulus", which may then develop fissures as a result. Because of the symmetry of the annulus, the centroid also lies at the origin. They can be identified by the light-blue sealant used on the primer annulus. In symmetric coaptation, leaflet tips meet at a common point on the annulus.