This image again shows some of the details of the upper respiratory tract of a cat.  Note that the walls of the larynx are supported by pieces of cartilage, the most prominent of which in this image is the thyroid cartilage, which forms the "Adam's apple".  Surrounding the thyroid cartilage is the thyroid gland, which belongs to the endocrine system.  Some of the cartilaginous C-shaped rings that provide support for the trachea so that its walls do not collapse and obstruct the passage of air can also be seen in the image.