. A laboratory manual and text-book of embryology. Embryology. THE THYMUS 171 According to Hammar (Arch. f. mikr. Anat., Bd. 61, 1903), the lateral pharyngeal recess (of Rosenmueller) is not a persistent portion of the second pouch as His asserted. Lymphocytes appear in the lymphoid tissue of the tonsils in embryos of 140 mm. They take their origin in the mesoderm (Hammar, Maximow). Palatine tonsil THE THYMUS bod^ The third, fourth and fifth pharyngeal pouches give rise to a series of ductless glands, of which the thymus is the most important. The thymus anlage appears in 10 mm. embr
. A laboratory manual and text-book of embryology. Embryology. THE THYMUS 171 According to Hammar (Arch. f. mikr. Anat., Bd. 61, 1903), the lateral pharyngeal recess (of Rosenmueller) is not a persistent portion of the second pouch as His asserted. Lymphocytes appear in the lymphoid tissue of the tonsils in embryos of 140 mm. They take their origin in the mesoderm (Hammar, Maximow). Palatine tonsil THE THYMUS bod^ The third, fourth and fifth pharyngeal pouches give rise to a series of ductless glands, of which the thymus is the most important. The thymus anlage appears in 10 mm. embryos as a ventral and medial prolongation of the third pair of pouches (Figs. 162 and 163). The ducts con- necting the diverticula with the pharynx soon disappear so that the thymus anlages are set free. At first hollow tubes, they soon lose their cavities, their lower ends enlarge and migrate caudally into the thorax passing usually ven-. Thymas anlaqes Post-branchial body Fig. 163.—Diagram in ventral view of the pharynx and pharyngeal pouches, showing the origin of the thymus and thyreoid glands and of the epithelial bodies (modified after Groschuff and Kohn). I, II, III, IV, and V, first, second, third, fourth and fifth pharyngeal Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Prentiss, Charles William, 1874-1915. Philadelphia, London, W. B. Saunders
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