Annulus

Annulus (diminutive from Latin anus), a ring, designation of ring-like formations. For example, A. femoralis ext. and int. - the external and internal openings of the so-called femoral canal, through which femoral hernias exit from the abdominal cavity to the thigh. - A. femor. ext. is the subcutaneous ring, bordered by tendon fibers of the sartorius aponeurosis of the thigh fascia and closed in front by its superficial sheet connected with them, which is pierced here by vessels (among them the v. saphena magna) and nerve branches (fascia cribrosa); A. fem. int. is bounded medially by the edge of lig. Gimbernatii (lig. lacunare), above by the Poupart ligament, below by the pectineal line, and laterally by the femoral vein. From the side of the pelvic peritoneum, the ring is closed by a connective tissue membrane (septum Cloqueti). Some authors consider it part of the fascia transversalis, others associate it with the prevesical fascia (fascia praevesicalis). In the area of this ring, Rosenmüller's lymph gland may be found. In cases of abnormal origin of art. obturatoriae from art. epigastrica inf., this ring is surrounded by blood vessels (aa. epigastrica and obturatoria, vv. obturatoria and femoralis). The danger created thereby during femoral hernia operation is characterized by the old name for this anomaly 'corona mortis.' - A. fibro-cartilagineus tympani - the fibrocartilaginous ring, with the help of which the tympanic membrane is fixed in the sulcus tympani. - A. fibrosus - the connective tissue margin along the edge of the opening, on the right - circular, on the left - horseshoe-shaped, to which the tricuspid and bicuspid valves of the heart are attached. - A. inguinalis ext. and int. - the external and internal 'openings' of the inguinal canal (see Inguinal canal). - A. tendineus communis (Zinnii) - the tendinous funnel-shaped ring, fixed at the apex of the orbital cone, serves as the place of origin of the straight muscles of the eye. - A. tympanicus - the flat bony semicircle, pars tympanica of the temporal bone of a newborn; from it later develops the part of the external auditory canal.