SB 10.2.27

ekāyano ’sau dvi-phalas tri-mūlaś
 catū-rasaḥ pañca-vidhaḥ ṣaḍ-ātmā
sapta-tvag aṣṭa-viṭapo navākṣo
 daśa-cchadī dvi-khago hy ādi-vṛkṣaḥ
Word for word: 
eka-ayanaḥ — the body of an ordinary living being is fully dependent on the material elements; asau — that; dvi-phalaḥ — in this body we are subject to material happiness and distress, which result from karma; tri-mūlaḥ — having three roots, the three modes of nature (goodness, passion and ignorance), upon which the body is created; catuḥ-rasaḥ — four rasas, or tastes*; pañca-vidhaḥ — consisting of five senses for acquiring knowledge (the eyes, ears, nose, tongue and touch); ṣaṭ-ātmā — six circumstances (lamentation, illusion, old age, death, hunger and thirst); sapta-tvak — having seven coverings (skin, blood, muscle, fat, bone, marrow and semen); aṣṭa-viṭapaḥ — — eight branches (the five gross elements — earth, water, fire, air and ether — and also the mind, intelligence and ego); nava-akṣaḥ — nine holes; daśa-chadī — ten kinds of life air, resembling the leaves of a tree; dvi-khagaḥ — two birds (the individual soul and the Supersoul); hi — indeed; ādi-vṛkṣaḥ — this is the original tree or construction of the material body, whether individual or universal.
Translation: 
The body [the total body and the individual body are of the same composition] may figuratively be called “the original tree.” From this tree, which fully depends on the ground of material nature, come two kinds of fruit — the enjoyment of happiness and the suffering of distress. The cause of the tree, forming its three roots, is association with the three modes of material nature — goodness, passion and ignorance. The fruits of bodily happiness have four tastes — religiosity, economic development, sense gratification and liberation — which are experienced through five senses for acquiring knowledge in the midst of six circumstances: lamentation, illusion, old age, death, hunger and thirst. The seven layers of bark covering the tree are skin, blood, muscle, fat, bone, marrow and semen, and the eight branches of the tree are the five gross and three subtle elements — earth, water, fire, air, ether, mind, intelligence and false ego. The tree of the body has nine hollows — the eyes, the ears, the nostrils, the mouth, the rectum and the genitals — and ten leaves, the ten airs passing through the body. In this tree of the body there are two birds: one is the individual soul, and the other is the Supersoul.
Purport: 

This material world is composed of five principal elements — earth, water, fire, air and ether — all of which are emanations from Kṛṣṇa. Although materialistic scientists may accept these five primary elements as the cause of the material manifestation, these elements in their gross and subtle states are produced by Kṛṣṇa, whose marginal potency also produces the living entities working within this material world. The Seventh Chapter of Bhagavad-gītā clearly states that the entire cosmic manifestation is a combination of two of Kṛṣṇa’s energies — the superior energy and the inferior energy. The living entities are the superior energy, and the inanimate material elements are His inferior energy. In the dormant stage, everything rests in Kṛṣṇa.

Material scientists cannot give such a thorough analysis of the material structure of the body. The analysis of the material scientists concerns itself only with inanimate matter, but this is inadequate because the living entity is completely separate from the material bodily structure. In Bhagavad-gītā (7.5) the Lord says:

apareyam itas tv anyāṁ
 prakṛtiṁ viddhi me parām
jīva-bhūtāṁ mahā-bāho
 yayedaṁ dhāryate jagat

“Besides this inferior nature, O mighty-armed Arjuna, there is a superior energy of Mine, which consists of all the living entities who are struggling with material nature and are sustaining the universe.” Although the material elements emanate from the Supreme Personality of Godhead, Kṛṣṇa, they are separated elements and are sustained by the living elements.

As indicated by the word dvi-khagaḥ, the living elements within the body resemble two birds in a tree. Kha means “sky,” and ga means “one who flies.” Thus the word dvi-khagaḥ refers to birds. In the tree of the body there are two birds, or two living elements, and they are always different. In Bhagavad-gītā (13.3), the Lord says, kṣetra-jñaṁ cāpi māṁ viddhi sarva-kṣetreṣu bhārata: “O scion of Bharata, you should understand that I am also the knower in all bodies.” The kṣetra jña, the owner of the body, is also called the khaga, the living entity. Within the body there are two such kṣetra jñas — the individual soul and the Supersoul. The individual soul is the owner of his individual body, but the Supersoul is present within the bodies of all living entities. Such a thorough analysis and understanding of the bodily structure cannot be obtained anywhere but in the Vedic literature.

When two birds enter a tree, one may foolishly think that the birds become one or merge with the tree, but actually they do not. Rather, each bird keeps its individual identity. Similarly, the individual soul and the Supersoul do not become one, nor do they merge with matter. The living entity lives close to matter, but this does not mean that he merges or mixes with it (asaṅgo hy ayaṁ puruṣaḥ), although material scientists mistakenly see the organic and inorganic, or animate and inanimate, to be mixed.

Vedic knowledge has been kept imprisoned or concealed, but every human being needs to understand it in truth. The modern civilization of ignorance is simply engaged in analyzing the body, and thus people come to the erroneous conclusion that the living force within the body is generated under certain material conditions. People have no information of the soul, but this verse gives the perfect explanation that there are two living forces (dvi-khaga): the individual soul and the Supersoul. The Supersoul is present in every body (īśvaraḥ sarva-bhūtānāṁ hṛd-deśe ’rjuna tiṣṭhati), whereas the individual soul is situated only in his own body (dehī) and is transmigrating from one body to another.