== Thyroid ==

The thyroid consists of two separate lateral lobes and a connecting part, the isthmus, lying over the superficial part of the trachea just below the larynx. Embryologically, the thyroid is derived as a diverticulum (thyroid diverticulum) from the midventral floor of the pharynx (entoderm).

== Parathyroid ==

In most individuals there are four parathyroid glands lying on the dorsal portion of the thyroid, embedded in a true capsule, thus separate from the thyroid. Ectopic parathyroids may be found anywhere from the base of the skull to the arch of the aorta, specifically in the thymus, in the cervical area external to the thyroid and in the mediastinum. The parathyroids have a rich blood supply although not as extensive as the thyroid. Developmentally, the superior pair of parathyroids forms from the endodermal 4th pharyngeal pouches (these parathyroids referred to as parathyroids IV); the inferior pair develop from the 3rd pharyngeal pouches (parathyroids III), as does the thymus. This fact explains the ectopic or aberrant occurrence of parathyroids in the thymus.

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== Suprarenal (Adrenal) Glands ==

The suprarenal glands (adrenal glands) are one of the major homeostatic organs of the mammalian body. They are composed of two separate endocrine organs that differ in embryological origin, type of secretion and function. In mammals, the two organs are arranged as an outer cortex and an inner medulla surrounded by a common capsule.