We investigated 100 skulls and found in 8 cases a dehiscence of the paries jugularis. In 7 cases this was on the left side and in 1 case on the right. Thickness of the paries jugularis was estimated by means of a diaphanoscopic technique. We classified data according to four degrees of diaphaneity: 0 (hardly translucent), 1 (translucent), 2 (brightly translucent) and 3 (nearly transparent). The frequencies of these degrees were: 0, 38 cases (19%); 1, 122 cases (61%); 2, 35 cases (17.5%); and 3, 5 cases (2.5%). In investigating the frequency of additional ducts in the paries jugularis, we distinguished between three types of solum tympani: type I, no additional canals (18 cases); type II, 1-10 additional canals (172 cases); and type III, more than 10 additional canals (10 cases).