Lobes of thyroid gland

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Lobes of thyroid gland
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The thyroid gland and its relations. (Lateral lobe labeled at center left.)
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Latin Lobuli glandulae thyreoideae
Gray's p.1269

The lobes of the thyroid gland makes of the bulk of the thyroid gland. There are normally two lobes; a right and a left, connected via the isthmus. Occasional, a third lobe, the pyramidal lobe, may be present in some individuals.

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 lower thirds of the right and left lobes of the thyroid gland are connects together via the isthmus.

The lateral or superficial surface of the lobes is convex, and covered by the skin, the superficial and deep fasciae, 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, the thyroid and cricoid cartilages, the trachea, the constrictor pharyngis inferior and posterior part of the cricothyreoideus muscles, 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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