The Compendium of Caraka 6.15.31

6.15.31

kharatvaṃ prakarotyasya jāyate 'asthi tato nṛṇām/
karoti tatra sauṣiryamasthnāṃ madhye samīraṇaḥ//

produces its roughness; bone is then born from it for men. / Wind produces porosity there in the middle of the bones;