Shatapatha Brahmana 6.6.1.24

6.6.1.24

śaṇakulāyamantaram bhavati | ādipyāditi nveva yadveva śaṇakulāyam prajāpatiryasyai yonerasṛjyata tasyā umā ulbamāsañcaṇā jarāyu tasmātte pūtayo jarāyu hi te na vai jarāyu garbhaṃ hinastyahiṃsāyai jarāyuṇo vai jāyamāno jāyate jarāyuṇo jāyamāno jāyātā iti

Inside there is a layer of hemp, just for the purpose that it may blaze up. And as to its being a layer of hemp,--the inner membrane (amnion) of the womb from which Pragâpati was born consists of flax, and the outer membrane (chorion) of hemp: hence the latter is foul-smelling, for it is the outer membrane of the embryo. [It is so used] to avoid injury, for the outer membrane does not injure the embryo; and it is from the outer membrane of the embryo that he who is born is born: 'May he (Agni), when he is born, be born from the outer membrane of the embryo!' thus he thinks.