To have a pictorial view of the extent of large paired sinuses of the posterior cranial fossa, jugular foramens, temporomandibular joints, magnetic resonance imaging and computed tomography were used to examine 1600 patients. The findings specified that the cross sizes of sinuses and jugular veins rather widely varied, their relative increase being observed with age. Furthermore, in most cases the paired sinuses of the posterior cranial fossa, internal jugular veins and jugular foramens are asymmetrically developed, the asymmetry being clearly defined only in infants aged more than 1 year. Thereafter, a group of patients with the asymmetrical structure ofjugular foramens was observed to have the signs characterizing the atypical structure or position of the heads of the mandible.