The development of the human body; a manual of human embryology . as those of the thyreoids,nor do they become separated into follicles, so that the THE BRANCHIAL EPITHELIAL BODIES. 315 pthm IV thm 1V pthm III bodies are readily distinguishable by their structure fromthe thyreoid. From the posterior wall of the third branchial groove apair of evaginationsdevelop, similar tothose which producethe lateral elongate great-ly, and growing down-ward ventrally to thethyreoid and separat-ing from their pointsof origin, come to liebelow the thyreoids,forming the thymusgland (Fig. 165, t
The development of the human body; a manual of human embryology . as those of the thyreoids,nor do they become separated into follicles, so that the THE BRANCHIAL EPITHELIAL BODIES. 315 pthm IV thm 1V pthm III bodies are readily distinguishable by their structure fromthe thyreoid. From the posterior wall of the third branchial groove apair of evaginationsdevelop, similar tothose which producethe lateral elongate great-ly, and growing down-ward ventrally to thethyreoid and separat-ing from their pointsof origin, come to liebelow the thyreoids,forming the thymusgland (Fig. 165, thy).As development pro-ceeds they passfurther backward andcome eventually torest upon the anteriorsurface of the peri-cardium. The cavitywhich they at firstcontain is early oblit-erated and the glandsassume a lobed ap-pearance and becometraversed by trabe-culae of connectivetissue. Lymphocytes, derived, according to some recent observations, directlyfrom the epithelium of the glands, make their appearanceand gradually increase in number until the original epi-. Fig. 166.—Thyreoid, Thymus and Epi-thelial Bodies of a New-bornChild. pthm III and pthm IV, Parathyreoids; sd,thyreoid; thm III, thymus; thm IV,lateral thyreoid.—(Groschujf.) 316 THE DEVELOPMENT OF THE HUMAN BODY. thelial cells are represented only by a number of peculiarspherical structures, consisting of cells arranged in con-centric layers and known as Hassals corpuscles. The glands persist until about the second year afterbirth, when they undergo a degeneration into a mass offibrous and adipose tissue.
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
