These three are internal compared to the previous ones.

Traya is the three: dhāraṇā, dhyāna, and samādhi. Antaraṅga means internal, intimate. Pūrva means previous, prior.

The first five limbs (yama, niyama, āsana, prāṇāyāma, pratyāhāra) are bahiraṅga, external. The last three are antaraṅga, internal.

The distinction is not hierarchical but functional. The external ones prepare the conditions; the internal ones perform the direct work on the mind.

Without the foundation of the external limbs, the internal ones cannot be sustained. Without ethics, without bodily discipline, without control of vital energy, the mind cannot concentrate stably.

But there is another reading: what is internal for one level is external for a deeper one. Everything is relative to the point of view.

The external limbs are practiced with the body and conduct. The internal ones are practiced exclusively with the mind. It is the difference between preparing the instrument and playing it.