**Core Concept**
The greater vein of Galen is a vital venous structure in the brain that plays a crucial role in draining the cerebrum and basal ganglia. It is a part of the deep cerebral venous system, which is responsible for draining the deep structures of the brain.

**Why the Correct Answer is Right**
The greater vein of Galen is formed by the junction of the internal cerebral veins (ICVs) and the basal veins of Rosenthal (BVRs). The ICVs are formed by the confluence of the medial and lateral choroidal veins, as well as the thalamostriate veins. The BVRs are formed by the junction of the anterior cerebral veins and the anterior choroidal veins. The fusion of the ICVs and BVRs gives rise to the greater vein of Galen, which then drains into the straight sinus.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the great cerebral vein of Galen is not formed by the union of the deep cerebral veins and the superficial cerebral veins. The superficial cerebral veins drain into the transverse sinus, not the great cerebral vein of Galen.
**Option B:** This option is incorrect because the internal cerebral veins do not drain into the great cerebral vein of Galen on their own; they must merge with the basal veins of Rosenthal to form the great cerebral vein of Galen.
**Option C:** This option is incorrect because the great cerebral vein of Galen is not a direct continuation of the straight sinus; it is a separate venous structure that drains into the straight sinus.

**Clinical Pearl / High-Yield Fact**
The great cerebral vein of Galen is a key landmark in neurosurgical procedures, particularly in the removal of brain tumors or aneurysms in the region of the basal ganglia and thalamus.

**Correct Answer:** C.