The Lord breathed on His disciples, and said, Receive ye the Holy
     Spirit (John 20:22);

for the same reason it is said that: 

     Jehovah God breathed into the nostrils of Adam the breath of lives,
     and he was made into a living soul (Gen. 2:7);

also He said to the prophet: 

     Prophesy upon the breath, and say unto the wind, Come from the four
     winds, O breath, and breathe upon these slain, that they may live
     (Ezek. 37:9);

likewise in other places; therefore the Lord is called “the breath of the nostrils,” and “the breath of life.”  Because respiration passes through the nostrils, perception is signified by them; and an intelligent man is said to be keen-scented, and an unintelligent man to be dull-scented.  For the same reason, spirit and wind in the Hebrew, and in some other languages, are the same word; for the word spirit is derived from a word that means breathing; and therefore when a man dies he is said to give up the ghost [anima].  It is for the same reason that men believe the spirit to be wind, or an airy something like breath breathed out from the lungs, and the soul to be of like nature.  From all this it can be seen that to “love God with all the heart and all the soul” means to love Him with all the love and with all the understanding, and to “give a new heart and a new spirit” means to give a new will and a new understanding.  Because “spirit” signifies understanding, it is said of Bezaleel: 

     That he was filled with the spirit of wisdom, of intelligence, and
     of knowledge (Exod. 31:3);

and of Joshua: 

     That he was filled with the spirit of wisdom (Deut. 34:9);

and Nebuchadnezzar says of Daniel: 

     That an excellent spirit of knowledge, of intelligence, and of
     wisdom, was in him (Dan. 5:11, 12, 14);

and it is said in Isaiah: 

     They that err in spirit shall learn intelligence (29:24);

likewise in many other places.

384.  Since all things of the mind have relation to the will and understanding, and all things of the body to the heart and lungs, there are in the head two brains, distinct from each other as will and understanding are distinct.  The cerebellum is especially the organ of the will, and the cerebrum of the understanding.  Likewise the heart and lungs in the body are distinct from the remaining parts there.  They are separated by the diaphragm, and are enveloped by their own covering, called the pleura, and form that part of the body called the chest.  In the other parts of the body, called members, organs, and viscera, there is a joining together of the two, and thus there are pairs; for instance, the arms, hands, loins, feet, eyes, and nostrils; and within the body the kidneys, ureters, and testicles; and the viscera which are not in pairs are divided into right and left.  Moreover, the brain itself