Śatapatha Brāhmaṇa ("of a hundred paths") 10.2.1.6

10.2.1.6

sa tasminnirṇāme ekāmiṣṭakāmupadadhāti tadyeyaṃ vayasaḥ patato nirṇāmādekā nāḍyupaśete tāṃ tatkarotyatho idam

On that bending-limb he places one brick he thereby gives to it that single tube (tubular organ) which joins on to (the body) from the bending-limb of the flying bird. Then here (on the left wing).