Complex sentence: The Superior Cerebral Veins, eight to twelve in number, drain the superior, lateral, and medial surfaces of the hemispheres, and are mainly lodged in the sulci between the gyri, but some run across the gyri.
Split into simpler sentences: The Superior Cerebral Veins, numbering eight to twelve, drain the superior, lateral, and medial surfaces of the hemispheres. They are predominantly found in the sulci between the gyri, but can also be found running across the gyri.