It describes the births of the graet Vasus in the house of Shantanu in the womb of Bhagirathi and their again going to heaven.
वसूनां पुनरुत्पत्तिर्भागीरथ्यां महात्मनाम्। शान्तनोर्वेश्मनि पुनस्तेषां चारोहणं दिवि॥