. The endocrine organs; an introduction to the study of internal secretion . e,1908; L. Lannoy, Thi/roides, Parathyroides, Thymus, 1914. For the parathyroids, seeD. A. Welsh, Journ. Anat., 1898 ; D. Forsyth, Trans. Path. Sue., 1907 ; and Guleke, Chirurgieder Nebenschilddrusen, 1913. r/tyro/cf FIG. 2.— Diagram to illustrate the origin of the cleft organs(thyroid, parathyroids, thymus, etc.) in the mammalianembryo. I, II, III IV, branchial pouches; , origin of lowerparathyroid from cephalic aspect of third poiu-h ; ,origin of upper parathyroid from cephalic aspect of four
. The endocrine organs; an introduction to the study of internal secretion . e,1908; L. Lannoy, Thi/roides, Parathyroides, Thymus, 1914. For the parathyroids, seeD. A. Welsh, Journ. Anat., 1898 ; D. Forsyth, Trans. Path. Sue., 1907 ; and Guleke, Chirurgieder Nebenschilddrusen, 1913. r/tyro/cf FIG. 2.— Diagram to illustrate the origin of the cleft organs(thyroid, parathyroids, thymus, etc.) in the mammalianembryo. I, II, III IV, branchial pouches; , origin of lowerparathyroid from cephalic aspect of third poiu-h ; ,origin of upper parathyroid from cephalic aspect of fourthpouch ; ,iv, origin of thymus from caudal aspect ofthird and fourth pouches ( usually forms the partassociated with the thyroid); , post-branchialbody, which forms a separate organ in lower Vertebrata,but in mammals either disappears or is incorporated withthe thjroid. •Structure of Thyroid 13 solid substance by fixative reagents. The intervesicular substance isareolar tissue, containing in parts many small cells. Some of these are. FIG. 3.—Section of thyroid (cat). Magnified 300 diameters. lymphocytes, whilst others are not unlike those of the parathyroids,although the identity has not been established. There are also verynumerous blood-vessels, the thyroid being one of the most vascular organsin the body; it receives in proportion to its sizemore than five times as much blood as thekidneys. The capillaries form a close networkaround each vesicle, giving a characteristic ap-pearance to an injected specimen (fig. 4): theycome into immediate contact with the vesicularepithelium (fig. 5). There are numerous lym-phatics within the organ, and colloid likethat of the vesicles is occasionally seen withinthem. The gland receives nerves from thesympathetic and from the superior and inferiorlaryngeal: they are distributed both to the blood-vessels and to the secreting epithelium. The vesicles of the thyroid do not always
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