The main osseous landmarks of the border area between the infratemporal fossa and the para- and retro pharyngeal space are the sphenoidal spine and the pterygoid and styloid processes, and the styloid vagina. These landmarks, as well as some vascular anomalies, were studied in order to illustrate the variable anatomy, which is encountered in the surgical lateral transzygomatic infratemporal fossa approach. Hundred well-preserved human skull bases were examined. The deep infratemporal fossa was dissected into 54 halves of fixed cadaveric head and neck specimens of both sexes. Dry skull specimens of New and Old World monkeys, skulls of rodents, herbivora and carnivora, and computed tomograms of the head of Macaca fuscata Japonica, were also studied. In 91 of the human skull bases, the sphenoidal spine was prominent and well developed. In three skulls, the spine was absent. In four specimens, however, the spine was not sphenoidal but a part of the temporal bone, occurring in the form of a process, which emanated from the styloid vagina. In two further cases, there was unilaterally a duplicated spine; the anterior part represented a regular sphenoidal spine, while the posterior part constituted a part of the vagina of the styloid process. A complete osseous bar, arch or lamina—connecting the posterior border of the lateral lamina of the pterygoid process and the sphenoidal spine—existed in six of the human dry skulls. In ten of the human skulls examined, the breadth of the lateral lamina of the pterygoid process was greater than 10 mm; thus, the so-called pterygospinous (ps) and the pterygostyloid gates—of significance where surgical approaches are concerned—were less than 10 mm in width. Fibrous or muscular connections were also found in some cadaveric specimens between the posterior border of the lateral lamina of the pterygoid process and the sphenoidal spine: a ps ligament existed in 11 cases (20.4%) and a ps muscle in 5 cases (9.2 %), in 3 of which it inserted into both the medial wall capsule and the articular disc of the temporo-mandibular joint. Among the cadaveric specimens exhibiting ps structures was one in which an osseous ps bar occurred together with a ps muscle; in two cases a strong ps ligament was observed together with a ps muscle. The distribution pattern of the mandibular nerve was affected by the positioning of the ps bar, ligament and muscle when the latter were present. The existence of a wide ps bar was noted in all the skulls of herbivora, rodentia, carnivora, and Old World monkeys that were examined, but never in those of the New World monkeys; it is likely that, in the human, this ps bar represents a phylogenetic remnant. In the human dry skull specimens and cadaveric material, the ps ligament was found to be a reinforcement of the interpterygoid fascia, and the ps muscle to be a third head of the lateral pterygoid muscle. In two cases, the internal carotid artery exhibited a significant elongation and space-consuming tortuosity (so-called coiling behavior) in the depth of the infratemporal fossa.
