The development of the human body; a manual of human embryology . econd disappears in its upperpart, the lower persisting as thegroove of Rosenmilller and thefossa in which the tonsil is situ-ated; while the remaining twodisappear, leaving traces of theirexistence in detached portionsof their epithelium which formwhat are termed the branchialepithelial bodies, among whichare the thyreoid and thymusglands. In the floor of the pharynxbehind the thickenings whichproduce the tongue there is tobe found in early stages a pair of thickenings passing horizontally backward and unit-ing in front so that
The development of the human body; a manual of human embryology . econd disappears in its upperpart, the lower persisting as thegroove of Rosenmilller and thefossa in which the tonsil is situ-ated; while the remaining twodisappear, leaving traces of theirexistence in detached portionsof their epithelium which formwhat are termed the branchialepithelial bodies, among whichare the thyreoid and thymusglands. In the floor of the pharynxbehind the thickenings whichproduce the tongue there is tobe found in early stages a pair of thickenings passing horizontally backward and unit-ing in front so that they resemble an inverted fj (, /). These ridges, which form what is termed thefurcula (His), are concerned in the formation of parts ofthe larynx (see p. 355). In the part of the roof of thepharynx which comes to lie between the openings of theEustachian tubes, a collection of lymphatic tissue takesplace beneath the mucous membrane, forming thepharyngeal tonsil, and immediately behind this there isformed in the median line an upwardly projecting pouch,. Fig. 164.—The Floor ofthe Pharynx of an Em-bryo op MM. /, Furcula; /, median portionof tongue.—(His.) 312 THE DEVELOPMENT OF THE HUMAN BODY. the pharyngeal bursa, first certainly noticeable in em-bryos mm. in length. This bursa has very generally been regarded as the persistentremains of Rathkes pouch (p. 300), especially since it is muchmore pronounced in fetal than in adult life. It has been shown,however, that it is formed quite independently of and posteriorto the true Rathkes pouch (Killian), though what its signifi-cance may be is still uncertain. The tonsils are formed from the epithelium of the lowerpart of the second branchial groove. At about the fourthmonth solid buds begin to grow from the epithelium intothe subjacent mesenchyme, and depressions appear on thesurface of this region. I^ater the buds become hollow bya cornification of their central cells, and open upon thefloor of the depressions w
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
