The development and morphological structure of the lateral sellar compartment (LSC), an interdural space containing the cavernous sinus (CS), cranial nerves, and internal carotid artery (ICA), was investigated by histological examination of sections of the LSC and cerebral venograms from human fetal specimens. Twenty-eight LSC coronal sections were obtained from 14 fetuses of 13-32 weeks’ gestation. Venograms of 11 other fetuses of 13-32 weeks’ gestation were studied to observe changes in venous drainage. The CS appeared as a collection of small venous canals with an endothelial layer. These venous canals gradually became much larger through expansion and unification. The CS and basilar venous plexus were demonstrated as a faint cluster of small vessels on venograms obtained after 13 weeks’ gestation. The dura mater increased in thickness and collagen fiber networks developed around all the components in the LSC after 23 weeks’ gestation. The LSC lateral wall could not be histologically differentiated as separate multiple layers. Branching and joining of the cranial nerve fascicles were completed with the envelopment of collagen fibers after 23 weeks’ gestation. The ICA at 13-15 weeks’ gestation ran straight within the LSC, becoming tortuous before birth. CS formation occurs through the development of venous canals without smooth muscle layers, followed by web-formation by collagen fibers in the mesenchymal interstices. LSC formation, including the dense dura mater and an internal structure like that seen in the adult, is largely completed before birth.