nadyo ’sya nirabhidyanta
tabhyo lohitam abhrtam
nadyas tatah samabhavann
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The veins of the universal body became manifested and thereafter the red corpuscles, or blood. In their wake came the rivers (the deities presiding over the veins), and then appeared an abdomen.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Blood veins are compared to rivers; when the veins were manifested in the universal form, the rivers in the various planets were also manifested. The controlling deity of the rivers is also the controlling deity of the nervous system. In Ayurvedic treatment, those who are suffering from the disease of nervous instability are recommended to take a bath by dipping into a flowing river.