This investigation was designed to extend our present knowledge of the origin of the anterior spinal a. and is based on 80 brains of human cadavers. The anterior spinal a. is usually formed rostrally by the union of the anterior spinal branches from the intracranial segments of the vertebral aa. In this study, we observed three different locations of the origin of the anterior spinal a. Each type has different characteristics. A bilateral origin (type I) was present in 60 specimens (75%). This type could be further subdivided according to the caliber of the arteries, into the following subtypes: "balanced" (type Ia 42.5%), right-dominated (type Ib 17.5%), and left-dominated (type Ic 15%). A unilateral origin (type II) was found in 9 specimens (11.3%), and an origin in an intervertebral transverse anastomosis was demonstrated in 11 (13.8%). In all cases, the anterior spinal a. had an average caliber of 1.145 +/- 0.12 mm.

Variations in the shape and size of the sigmoid sulcus were investigated in 561 temporal bones (438 isolated temporal bones, 49 skull bases and 25 half skull bases) and measurements of related structures were made. Right-left differences were analysed. The sigmoid sulcus was significantly wider (12 mm) and longer (38 mm) in the skull bases, while no differences were observed in the isolated temporal bones. The distance from the most prominent point of the mastoid process to the Frankfort horizontal plane (FHP) was 33 mm; no right-left difference was found. The distance from the genu of the sigmoid sulcus to the external acoustic meatus was 24.06 mm on the right side and 24.74 mm on the left side and this difference is significant, being considerably longer on the left side. The jugular foramen diameter was 7.8 mm; no right-left difference was observed. The relationship of the mastoid air cells to the sulcus was analysed and air cells were found just behind the sulcus in 66% and behind and posterior to the sulcus in 5% of temporal bones.