Yoga Sutras 1.45
Patanjali, explained by Swami Vivekananda
सूक्ष्मविषयत्वञ्चालिङ्ग-पर्यवसानम् ॥
sūkṣmaviṣayatvañcāliṅga-paryavasānam
The finer objects end with the Pradhāna.
In plain words: These finer objects of meditation go all the way back to Pradhana, the first root of all nature. The teacher explains that everything except the true Self, including the mind and ego, counts as part of nature.
Swami Vivekananda explains
The gross objects are only the elements and everything manufactured out of them. The fine objects begin with the Tanmatras or fine particles. The organs, the mind, egoism, the mind-stuff (the cause of all manifestation), the equilibrium state of Sattva, Rajas, and Tamas materials — called Pradhāna (chief), Prakriti (nature), or Avyakta (unmanifest) — are all included within the category of fine objects, the Purusha (the Soul) along being excepted.