The development of the human body; a manual of human embryology . 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 Fig. 167.—Diagram sho
The development of the human body; a manual of human embryology . 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 Fig. 167.—Diagram showing the Origin of the Various Branchial Epithelial , Lateral thyreoids; pp, postbranchial bodies; pkt1 and pht2, para- thyreoids; th, median thyreoid; thy, thymus; I to IV, branchial grooves.—(Kohn.) Finally, a pair of outgrowths arise from the floor of thepharynx just behind the fifth branchial arch, in the regionwhere the fifth groove, if developed, would occur. Thesepost-branchial bodies, as they have been called, usuallyundergo degeneration at an early stage and disappearcompletely, though occasionally they persist as cysticstructures embedded in the substance of the thyreoid. THE (ESOPHAGUS. 317 The relation of these various structures to the branchialgrooves is shown by the annexed diagram (Fig. 167); and fromit, it will be seen that the bodies derived from the third andfourth grooves are serially equivalent. Comparative embry-ology makes this fact still more evident, since, in the lower ver-tebrates, each branchial groove contributes to the f
Size: 1674px × 1493px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
