Todt W L, Fallon J F
Anat Rec. 1986 Jul;215(3):288-304. doi: 10.1002/ar.1092150312.
Histologic examination of the leg bud of stage-18 to stage-23 chick embryos was carried out with special reference to the development of the apical ectodermal ridge. The leg bud apical ectoderm, initially an irregular columnar epithelium with an overlying simple squamous periderm, began to thicken during stage 18 and was a pseudostratified epithelium by stage 19. A notch in the base of the thickened ectoderm was seen as early as stage 19. The notch represented the cross-sectional view of a groove, which developed in the base of the ridge. As development proceeded, the ridge and its associated groove lengthened. In addition, the groove became more prominent, and irregularities were seen in its width and depth along the apex. Ectodermal cell death was not consistently seen until stage 21 at which time most of the length of the thickened ectoderm had evidence of necrosis. Development of the leg bud ridge and wing bud ridge were compared. The temporal sequence of ectodermal thickening and ridge development was very similar in both the leg and wing buds with one exception; namely, that leg bud ridge development preceded wing bud ridge development by several hours. In addition, ectodermal cell death was not evident until stage 20 in the leg bud ridge, but could be seen at late stage 18 in the wing bud apical ectoderm. However, by stage 21, cell death was associated with most of the ridge in both the wing and leg buds. Finally, with respect to the axial line, the ridge with its associated groove extended further preaxially in the leg bud than in the wing bud, making the leg bud ridge more symmetrical.
对18期至23期鸡胚的腿芽进行了组织学检查，特别关注顶端外胚层嵴的发育。腿芽顶端外胚层最初是一层不规则的柱状上皮，上面覆盖着单层扁平的周皮，在18期开始增厚，到19期时成为假复层上皮。早在19期就可见增厚外胚层基部有一个切迹。该切迹代表了在嵴基部形成的一条沟的横切面。随着发育的进行，嵴及其相关的沟延长。此外，沟变得更加明显，其沿顶端的宽度和深度出现不规则变化。直到21期才持续观察到外胚层细胞死亡，此时增厚外胚层的大部分长度都有坏死迹象。对腿芽嵴和翅芽嵴的发育进行了比较。外胚层增厚和嵴发育的时间顺序在腿芽和翅芽中非常相似，只有一个例外；即腿芽嵴的发育比翅芽嵴的发育提前几个小时。此外，腿芽嵴直到20期才出现明显的外胚层细胞死亡，但在翅芽顶端外胚层的18期末期就可以看到。然而，到21期时，翅芽和腿芽的大部分嵴都出现了细胞死亡。最后，就轴线而言，带有相关沟的嵴在腿芽中比在翅芽中更向轴前延伸，使腿芽嵴更对称。
