. A Reference handbook of the medical sciences : embracing the entire range of scientific and practical medicine and allied science. (ductus lingualis)persists as the foramen caecum, while the lower part(ductus thyroideus) becomes obliterated. He has de-tected traces of this portion in adults, and sometimes abody resembling the thyroid gland in structure has been called the suprahyoid or the prse-hyoidgland. The symmetrical or lateral centres for the thyroidgland, formed from the last branchial clefts, soon separatefrom their original attachments and fuse in the middle ofthe neck
. A Reference handbook of the medical sciences : embracing the entire range of scientific and practical medicine and allied science. (ductus lingualis)persists as the foramen caecum, while the lower part(ductus thyroideus) becomes obliterated. He has de-tected traces of this portion in adults, and sometimes abody resembling the thyroid gland in structure has been called the suprahyoid or the prse-hyoidgland. The symmetrical or lateral centres for the thyroidgland, formed from the last branchial clefts, soon separatefrom their original attachments and fuse in the middle ofthe neck about the trachea. In some animals {, dogsand horses) this fusion does not take place, consequentlythe thyroid in such animals possesses no isthmus. Insome reptiles the right lobe always remains first the thyroid consists of very small vesicles widelyseparated by a large amount of embryonic connectivetissue, but later the vesicles become larger and more nu-merous, while the connective tissue disappears. Anomalies.—The most common is the presence of aslender tongue-like process (see Fig. 3934) (middle lobe,. Fig. 3924.—Thyroid Gland with Middle Lobe Present. (Henle.) pyramid), extending upward in front of the larynx. Itoccurs in forty per cent, of all cases (Gruber). It isoften separated from the isthmus. When present, it often has a muscular slip attached toits anterior surface (levator glandulae thyroidese, or mus-culus azygos), usually derived from the thyro-hyoid. The isthmus is sometimes situated abnormally is of importance in performing tracheotomy, as itis sometimes convenient to draw down the isthmus in-stead of raising it, and perform the operation above theisthmus instead of below it. The isthmus is sometimes absent altogether in man,the gland then consisting of two lateral lobes only—whichis the normal condition in many of the mammalia. The lateral lobes sometimes extend abnormally high,even above the level of the hyoid bone. Inferior
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectmedicine, bookyear188
