. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 1104 THYROID GLAND. once have been considered that a gland should exist unprovided with an efferent duct. I now proceed to give a more detailed account of the structure of the thyroid gland. Its surface is somewhat uneven, — a natural condition which is often greatly exagge- rated in hypertrophy of the gland ; it is tra- versed by several large branches of the nutrient arteries, which ramify over it before they plunge into its substance. A thin fibrous expansion, continuous with the sheath of the cervical vessels on each
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 1104 THYROID GLAND. once have been considered that a gland should exist unprovided with an efferent duct. I now proceed to give a more detailed account of the structure of the thyroid gland. Its surface is somewhat uneven, — a natural condition which is often greatly exagge- rated in hypertrophy of the gland ; it is tra- versed by several large branches of the nutrient arteries, which ramify over it before they plunge into its substance. A thin fibrous expansion, continuous with the sheath of the cervical vessels on each side, forms a capsule which invests the gland, and from whose inner surface septa dip into the interior, dividing its substance into lobes and lobules much after the manner of a conglomerate gland ; these fibrous septa are often well seen in sections of hypertrophied specimens. A thin slice of the thyroid, examined under a low power of the microscope, displays its con- stitution very perfectly and readily '(fig. 733.) It is seen to be made up of closed vesicles, aggregated together in groups of various size by the fibrous expansions just described. The form of these vesicles is primarily spherical; but many, perhaps the majority, are more or less affected by mutual pressure, being trian- gular, elongated, ovoid, or oblong. They are all perfectly closed, the wall being formed by an homogeneous limitary membrane, which is easily traced all round, and can never be seen passing off into a neck, or blending with the envelope of an adjacent vesicle. Where a number of vesicles lie closely crowded to- gether, the homogeneous envelopes are of course in contact, or separated only by the interjacent vascular plexus ; but those form- ing the surface of a group are invested by a thin expansion of fibrous tissue derived from the general capsule. The diameter of the vesicles of the human thyroid I have found to range from ^-oVo incn to -gV Fie. '-4 group of vesicles from the tlnjroi
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