The lobes of the thyroid gland are conical in shape, the apex of each being directed upward and lateralward as far as the junction of the middle with the lower third of the thyroid cartilage; the base looks downward, and is on a level with the fifth or sixth tracheal ring. Each lobe is about 5 cm. long; its greatest width is about 3 cm. , and its thickness about 2 cm. The lateral or superficial surface is convex, and covered by the skin, the superficial and deep fasciæ, the Sternocleidomastoideus, the superior belly of the Omohyoideus, the Sternohyoideus and Sternothyreoideus, and beneath the last muscle by the pretracheal layer of the deep fascia, which forms a capsule for the gland. The deep or medial surface is moulded over the underlying structures, viz. , the thyroid and cricoid cartilages, the trachea, the Constrictor pharyngis inferior and posterior part of the Cricothyreoideus, the esophagus (particularly on the left side of the neck), the superior and inferior thyroid arteries, and the recurrent nerves. The anterior border is thin, and inclines obliquely from above downward toward the middle line of the neck, while the posterior border is thick and overlaps the common carotid artery, and, as a rule, the parathyroids

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uberon

lobuli glandulae thyroideae

Thus, a thyroid capable of forming iodotyrosines and iodothyronines is present in all vertebrates. (...) Certain morphologic changes occur after the biochemical evolution of the thyroid has ceased. In the adult lamprey and in most bony fishes, the gland is not encapsulated. (...) In cartilaginous fish, the thyroid is encapsulated. In the higher vertebrate forms, the thyroid is a one- or two-lobed encapsulated structure.[well established][VHOG]

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