The division of the human being into a body and a soul is quite insufficient to explain the structure of the human being. The Hindus consider that three main elements contribute to the formation of a living being. They are the Self or spirit, the subtle body and the gross body.
The Individual Self, or Atman is a fragment of the Total Being, indivisible and undifferentiated. Just as the space enclosed within a pitcher is in no way really differentiated from the rest of space, so likewise the fragment of the Universal Self enclosed within the human being remains the indivisible part of the Total Self.
This fragment of the Total Self is enclosed within seven sheaths, six of which pertain to the subtle body, the seventh being the gross body.
The subtle or transmigrating body is the essential part of the human individuality; made of seventeen elements, it remains when the body is destroyed and lives through the lengthy cycle of births and deaths until its dissolution at the time the living being reaches its aim of final liberation.
The subtle body is generally considered to be made of seventeen elements: five senses of perception, five senses of action, five vital energies, mind (manas) and intellect (Buddhi, which includes the "notion of I-ness", Ahamkara).
Just as the relation of the chrysalis to the butterfly, so the subtle body is inverted in regard to the gross body. Their relation is sometimes symbolized by two interwoven inverted triangles. This is why the most abstract state of subtle manifestation is found in the Root-center, the Muladhara chakra.
The subtle body is connected with the gross body at several points. These are called the knots or Centers and are sometimes represented as lotuses. In these Centers the subtle nerves and arteries of the subtle body are connected to the physical nerves through which they receive the perception of the sense organs and through which they communicate to the body the reaction of the subtle body and the orders of the Conscious.
Only the outer nerves of the subtle centers can be seen physically and their convergence observed.