The larynx, which lies between the pharynx (upper part of the air passages) and the trachea (windpipe), forms part of a tube in the throat that carries air to and from the lungs. 

It consists of areas of tough, flexible tissue called cartilage, which stick out at the front of the throat to form the Adam's apple. Below this, connecting the thyroid cartilage to the trachea is another cartilage which is shaped like a signet ring with the seal at the back of it. 

Just on top of this seal are two pyramid-shaped cartilages, and between these two cartilages and the inner surface of the Adam's apple stretch two fibrous sheets of tissue, called the "vocal cords, which are responsible for voice production. 

The larynx, or voice box, has the important function of preventing choking. When we are not eating or drinking, the epiglottis stays upright, keeping the larynx open as part of the airway to the lungs; as soon as swallowing begins, the epiglottis drops like a lid over the larynx, directing food to either side. Closing the vocal cords also helps to protect the air passage. 

The food or drink passes down the esophagus to the stomach. The second function of the larynx is voice production. Air from the lungs passes over the stretched vocal cords, and the vibrations are modified by the tongue, palate, and lips to produce speech. To hem and haw can be traced back to "humys and hays," a phrase that first appeared in print in 1469 and to "hem and hawke," which appeared in 1580. The words suggest the sound made when clearing the throat and allows one to delay before speaking or, perhaps, it expresses a kind of disapproval.