. Anatomischer Anzeiger. Anatomy, Comparative; Anatomy, Comparative. 563 of the small adductor arcuum branchialium. The genio-hyoidei, at either side of the thyroid outgrowth, pass from this section anteriorly into a dorsal plane, and posteriorly into a ventral plane. The thyroid outgrowth now bifurcates on the antherior wall of the pericardium. add th yh nih sh - pc. km el - km cl add hb cl Fig. 7. From two horizontal sections through the thyroid outgrowth in an embryo 15 mm long. add adductor arcuum branchiulium. gh genio-hyoideus. hbcl hyo- branchial cleft, hmcl base of hyomandibular pocket
. Anatomischer Anzeiger. Anatomy, Comparative; Anatomy, Comparative. 563 of the small adductor arcuum branchialium. The genio-hyoidei, at either side of the thyroid outgrowth, pass from this section anteriorly into a dorsal plane, and posteriorly into a ventral plane. The thyroid outgrowth now bifurcates on the antherior wall of the pericardium. add th yh nih sh - pc. km el - km cl add hb cl Fig. 7. From two horizontal sections through the thyroid outgrowth in an embryo 15 mm long. add adductor arcuum branchiulium. gh genio-hyoideus. hbcl hyo- branchial cleft, hmcl base of hyomandibular pocket, mh mylohyoideus, pc pericardium. *A sterno-hyoideus. th thyroid outgrowth. In sections through an embryo of 16 mm, the thyroid outgrowth is unchanged, but immediately after this stage, the outgrowth becomes irregularly broken in its median part so that the anterior and posterior parts are separate. Cells from the anterior part of the broken outgrowth wander downwards onto the dorsal surface of the mylohyoideal muscle, and are finally lost in muscular tissue. No accessory thyroid develops in this region. A few scattered cells from the anterior part of the outgrowth are also found above the level of the muscles genio-hyoidei, but the subsequent fate of these isolated cells could not be followed after their distinguishing yolk granules had disappeared. The division of the posterior part of the thyroid, begun in the embryo of 15 mm (fig. 7), continues, and in embryos of 17 and 18 mm, one finds in place of the solid thyroid outgrowth, two lines of cells extending obliquely outwards and upwards at the head of the adductor muscles, but forming neither a solid mass nor the walls of closed vesicles, These posterior cells of the thyroid outgrowth appear to migrate dorsalwards as mesenchyme, and may be distinguished in an embryo of 19 mm as a group of cells lying on each side of the embryo, between the lateral surface of the sterno-hyoideus and the cartilage of the first epibranchial, j
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