On the Body of the Virat

 It's the (primary) neural entity associated with the primary bronchus that seems to be "manas." The primary  bronchus  itself seems to be the body of the VIRAT; and the two upper and the two lower (lobar) bronchi seem to be the head and hands and the thighs and feet respectively. The four sides of Meru have the colours of the four castes; and as the four castes are held to emanate from the mouth, hands, thighs and feet of VIRAT; therefore it's logical to think that it's the lobar bronchi--the  four sides of Meru--that constitute the head and the limbs of VIRAT. Therefore the members of the four  castes are the neural entities belonging to these regions. This also provides a clue with regard to the division of the five islands beginning with Plaksa. As all four categories are present within each of these dvipas, each such entity must therefore include all four lobar regions. They probably indicate deeper and deeper levels of the hierarchy of the bronchial tree.