Todt W L, Fallon J F
J Embryol Exp Morphol. 1984 Apr;80:21-41.
Histological examination of the stage-18 to stage-23 chick wing bud apex revealed the following. Initially, the wing bud was covered by a cuboidal to columnar epithelium with an overlying periderm. Thickening of the apical ectoderm was not obvious until late stage 18 (36 pairs of somites), after the appearance of the wing bud. At late stage 18, cells of the inner layer of ectoderm had elongated slightly along an axis perpendicular to the epithelial-mesenchymal interface. Well-defined apical ectodermal ridge morphology, i.e., pseudostratified columnar epithelium with an overlying periderm, was not apparent until stage 20. Subsequently the ridge lengthened along the anteroposterior perimeter of the wing bud. We demonstrated histologically that the apical ectodermal ridge of the wing bud was asymmetric with respect to the anteroposterior axis, in that there was more ridge associated with posterior mesoderm. Other observations include the spatial and temporal location of a groove in the base of the thickest part of the ridge. The groove can be correlated with the specification of distal wing elements. The groove was first seen at stage 20 and became more prominent through stage 23. An anteroposterior progression of ectodermal cell death was also observed. This began at late stage 18 and continued through each of the stages examined.
对18期至23期鸡胚翼芽顶端进行组织学检查，结果如下。最初，翼芽被一层立方上皮至柱状上皮覆盖，其上方还有一层周皮。直到18期晚期（36对体节），翼芽出现后，顶端外胚层的增厚才变得明显。在18期晚期，外胚层内层细胞沿垂直于上皮-间充质界面的轴稍有伸长。直到20期，清晰的顶端外胚层嵴形态，即有周皮覆盖的假复层柱状上皮才明显可见。随后，嵴沿着翼芽的前后周长延长。我们通过组织学证明，翼芽的顶端外胚层嵴在前后轴上是不对称的，即与后中胚层相关的嵴更多。其他观察结果包括嵴最厚部分基部一条沟的空间和时间位置。这条沟与远端翼元件的特化有关。这条沟在20期首次出现，并在23期变得更加明显。还观察到外胚层细胞死亡的前后进展。这始于18期晚期，并在每个检查阶段持续存在。
