A Reference handbook of the medical sciences embracing the entire range of scientific and practical medicine and allied science . ion of a Human Em-bryo, Five Weeks Old. (From Minot, after His.) //. ///. IV,Branchial arches; Sp, second branchial grooves; lyj. inf uudibulumpraecervicale; F, fundus of the infundibulum : 3, 4, third andfourth branchial pockets, with the thymus arising from the third;^0^, Ao*, aortic arches ; Ep., epiglottis ; IX, glosso-pharyngealnerve ganglion; XII, hypoglossal nene; id, superior laryngealnerve. sends two horns which extend on either side of the neckto the thyro
A Reference handbook of the medical sciences embracing the entire range of scientific and practical medicine and allied science . ion of a Human Em-bryo, Five Weeks Old. (From Minot, after His.) //. ///. IV,Branchial arches; Sp, second branchial grooves; lyj. inf uudibulumpraecervicale; F, fundus of the infundibulum : 3, 4, third andfourth branchial pockets, with the thymus arising from the third;^0^, Ao*, aortic arches ; Ep., epiglottis ; IX, glosso-pharyngealnerve ganglion; XII, hypoglossal nene; id, superior laryngealnerve. sends two horns which extend on either side of the neckto the thyroid, as is the case in the birds. From now on,the organ gradually atrophies. In the study of the human embryo Sudler finds noindication of the thymus in a human embryo of the sec-ond week, but in one of the fourth week the third vis-ceral pouch appears as a ridge with a ventral free end,with uo differentiation of tissue to suggest a thymus. In 569 Thymus Gland. REFERENCE HANDBOOK OF THE MEDICAL SCIENCES. an embryo four and one-half weeks old this ridge hasdisap]icarcd and tlie third visceral pouch ]irojects out. Fig. 533(1.—Reconstruction of a Human Embryo Four Weeks old.(No. 2.) Enlarge(J sLxteen times, and viewed from the left side. H,Hypophysis: 1, 2, 3, and i, branchial pockets: M. mouth : A. auri-cle : V, ventricle; AD, descending aorta : L, lung: S, stomach:P, pancreas. directly from the pharynx (Fig. 52321. In the nextstage, of about five weeks, it is very similar to one de-scribed by Born, in which thethymus has become completelyseparated from the pharynx, andits original hollow is reduced to acrescent-shaped oijening which isquite characteristic of the glandat this stage. The thymus nowis a curved elongated body withan enlarged cephalic end. Thelower end of this and the thyroid(Fig. 5233) run parallel, thoughwithout coming in coutact witheach other till the thyroid bendsabruptl} and crosses the middleline. An embryo slightly oldershows practically the sa
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