Histological Studies of the Human Thyroid Gland in Middle and Late Prenatal Life

This paper contains the o b servations on thyroid glands of 70Japanese fetuses ranging in age from 95 mm (13 weeks) to 520 mm CHL (40 weeks), and the results obtained were as follows: 1) Thyroid glands are not solid and are composed of colloidcontaining follicles and primitive follicles. 2) Formation of lobules is no t always seen all over the gland, but only relatively distinct in the peripheral zone. 3) Follicles of various sizes are more or less extensively associated in the gland, but no open communication of their cavities was noted. Hence the follicular networks are formed within the thyroid parenchyma in relatively early stages of prenatal life. 4) Large follicles are associated more frequently with others and produce more numerous primitive follicles. 5) The large follicles and their surrounding associated follicles form an arboreal system, the “ Drüsenbäumchen. ” The large follicles represent trunks of trees and their surrounding associated follicles branches and roots. 6) The as s ociation of follicles may be interpreted as an indication of proliferation, present and past, of follicles. 7) The dissociation of follicles proceeds with age but is not completed even near term. 8) A dominant o c currence of the Zentralkanälchen within the lobule and Zylinderepithelschläuche without relation in position to the lobule can not be interpreted as a constant and common pattern in the development of the thyroid gland of Japanese fetuses. 9) The so-called “S anderson's Polster” or “ Proliferationsknospe” could not be found in the normal development of this gland. 10 ) Argyrophilic fibers were abundant, forming a perifollicular layer closely around the follicles, but no elastic fibers were found in the perifollicular spaces.