Variations and anomalies of the human orbital muscles.

The purpose of the study is to describe some rare and hitherto unreported uni- and bilateral anomalies of the orbital rectus muscles (duplication, triplication, accessory bellies, interrectal muscular bridges, false insertion) which were found by chance during the dissections of three cadavers (one adult, two fetuses). The levator palpebrae superioris muscles in the same specimens exhibited some variations (medial and lateral muscular slips) and anomalies (bipartite and unipartite levator). Cross-sections of interrectal bridges in the orbit of an adult were investigated histologically. Numerous nerves were distributed in the interstitium; groups of lipofuscin granules were found in all the myocytes. An attempt is made to explain these anomalies and variations through consideration of developmental and comparative anatomy. The relevance of these anomalies in coronal sections such as those acquired from CT and MRI is discussed.