Know that Drona was a portion of Brihaspati, and that Drona's son is born of a portion of Rudra. Know that Ganga's son Bhishma was one of the Vasus who became born as a men.
द्रोणं बृहस्पतेर्भागं विद्धि द्रौणिं च रुद्रजम्। भीष्मं च विद्धि गाङ्गेयं वसुं मानुषतां गतम्॥