THYROID BODY or GLAND (Gr. thyreos, a shield, and eidos, like), one of the ductless or vascular glands, lying at the upper part of the trachea, and consisting of two latteral lobes, placed one on each side of this canal, and connected together by a narrow trans verse portion at the lower third, called the isthmus. It is of a brownish red color, and its normal weight is about an ounce, but it occasionally becomes enormously enlarged, constituting the disease called bronchocele or goiter. Each lobe is somewhat conical, and is about two inches long and three-quarters of an inch broad. The thyroid. body differs from the other vascular glands in structure, for it " consists of an aggregation of closed vesicles, which seem to be furnished with a true limitary membrane, and there fore to be real gland vesicles embedded in a stroma of connective tissue, and not commu nicating- with any common reservoir. These bodies vary in diameter in the human sub ject to iy of an inch; and they contain an albuminoid plasma, which is either faintly or of a somewhat oily aspect, amid which are seen a number of corpus cles, the greater part of them in the condition of nuclei, while some have advanced to that of cells."—Carpenter's Principles of Ifunzan Physiology, 6 ed., p. 143. The thyroid body is abundantly supplied with blood by the superior and inferior thyroid arteries, which continue subdividing till they ultimately form a very minute capillary plexus upon the limitary membrane of the vesicles. This body, like the thymus and supra
renal capsules, is relatively larger in the fetus and during infancy than in after-life.
From the investigations of Mr. Simon (see his memoir on the "Comparative Anatomy of the Thyroid," in the Pitibsophical Transactions, for 1884), it appears that a thy roid is present in all mammals, birds, reptiles, and amphibians, and that he has discovered it in many fishes. Its presence in some of the fishes in which Mr. Simon observed it, has, however, been called in question by Dr. Handheld Jones, (see his article " Thyroid Gland " in the Cyclopedia of Anatomy and Physiology).
Mr. Simon has propounded a theory regarding the function of this gland which is certainly ingenious, and probably correct. Basing his theory on the circumstance, that the thyroid arteries arise in close proximity to the cerebral, he considers that the thyroid gland acts as a diverticulnin to the cerebral circulation, exercising at the same time its secreting function in an alternating manner with the brain.
Little need be said here regarding the diseases of this organ, as the most important of them, branchocele or goiter, has been already described under the latter title.