. The thyroid gland in health and disease. y by the two rows of cells forming their walls (fig. 1), and bythe vascular network surrounding them ; but much more com-monly they arc separated by a layer of cells of variable thickness(fig. 3). When the vesicles are small the intervesicular parenchymais more plentiful ; when they are larger it is correspondinglydiminished. Two sections from the same gland may thus varyconsiderably in appearance. Some authors divide the parenchyma cells of the thyroid into STRUCTURE 11 principal cells and colloid cells. Such a division is unneces-sary and misleading
. The thyroid gland in health and disease. y by the two rows of cells forming their walls (fig. 1), and bythe vascular network surrounding them ; but much more com-monly they arc separated by a layer of cells of variable thickness(fig. 3). When the vesicles are small the intervesicular parenchymais more plentiful ; when they are larger it is correspondinglydiminished. Two sections from the same gland may thus varyconsiderably in appearance. Some authors divide the parenchyma cells of the thyroid into STRUCTURE 11 principal cells and colloid cells. Such a division is unneces-sary and misleading since the different appearances representdifferent stages of the cells activity. All parenchyma cells,whether lining the vesicles or not, may, if occasion demands,form themselves into new vesicles and take part in the formationof the glands secretion. After death from acute infections. orpoisonings the cells lining the vesicles may become separatedfrom their basal The intervesicular tissue may, in addition to its parenchyma. Fig. 3.—Section of normal thyroid and parathyroid of young adult wild rat,showing the proportion of intervesicular tissue to vesicles usually met with inyoung thyroids. x 100. cells, contain portions of thymus tissue or of parathyroid small cells may be found scattered through it or arrangedin masses. Some of these are lymphocytes, others, found in morecompact masses, are the foetal rests from which foetaladenomata are said to arise. The Parathyroid Gland is composed of polygonal epithelium-like cells. The cells may be disposed in a retiform manner andseparated by an extremely delicate network of fibres (fig. 4) orthey may be arranged in compact masses ; both arrangementsmay be seen in the same glandule. Strands of connective tissue 12 HISTOLOGY AND PHYSIOLOGY from the areolar capsule of the gland, carrying with them theblood-vessels and nerves which supply the epithelium, divide theglandule into irregular lobules. These strands
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