Narapatijayacarya 3.1.11

3.1.11

suṣumrā nāḍī sā dehamadhyasthā brahṛmarandhragāminī śambhusvarūpiṇīti | haṃsasvarūpakaḥ śambhu iti | śaktirūpa iti | ślokadvayam sugamam ||

is the Suṣumnā subtle channel, situated in the middle of the body, going to the fontanelle (brahmarandhra), has the nature of Śambhu. 'Śambhu has the form of haṃsa'; 'having the nature of Śakti,' etc.: the two verses are easy to understand.