A Reference handbook of the medical sciences embracing the entire range of scientific and practical medicine and allied science . the branchial arches are well formed(Fig. 5235). This has been known since thetime of W. Muller, and, although contra-dicted many a time, has of late been verified by somany careful observers that there is no longer any doubtwhatever regarding it. In some mammals (the dog. forinstance) it arises as a vesicle, which becomes solid beforeit separates from the pharynx, and when separated soonbecomes lobulated. It now gradually shifts itself intothe tissue of the neck, a
A Reference handbook of the medical sciences embracing the entire range of scientific and practical medicine and allied science . the branchial arches are well formed(Fig. 5235). This has been known since thetime of W. Muller, and, although contra-dicted many a time, has of late been verified by somany careful observers that there is no longer any doubtwhatever regarding it. In some mammals (the dog. forinstance) it arises as a vesicle, which becomes solid beforeit separates from the pharynx, and when separated soonbecomes lobulated. It now gradually shifts itself intothe tissue of the neck, and in early stages lies in front ofthe aorta just as it leaves the heart (Fig. 5236). Themedian gland now becomes constricted into two parts,one of which is situated on either side of the neck, butthey remain connected by a band—the isthmus. Its ori-gin In the human embryo is much the same (Figs. 5337 ever, the formation of the ligamentum hypothyroideiuacuts the duct (rf. ihyreofflossus) into two, thus formingtwo ducts. The half communicating with tlie mouthhas been termed by His ductus linyualis, and the one with !im. Fig. 5238.—Reconstruction of the Thyroid, Thymus, and Pharynx ofa Human Embryo Five Weeks Old. (Slightly modified from His.)Uim. Thymus; thr, thyroid; c, carotid; ao, ascendinfc aorta;ai), descending aorta; t/., trachea. the thyroid as the ductns thywideiis. His has found theductus lingualis in five adults, and in all cases the duc-tus thyroideus was present also. The latter is alwayseiiibedded in a median lobe of the thyroid, and the formeropens into the foramen ciecum of the tongue. The duc-tus thyreoglossus may be broken into a series of vesicles,as first described by Verneuil, but as a rule it disappearsfully, its only remnant being the foramen coecuni.* The lateral thyroids were first demonstrated by Stiedaand by Born, although Rathke, His, and others had in all
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