Müller F, O'Rahilly R
Am J Anat. 1980 Sep;159(1):33-58. doi: 10.1002/aja.1001590105.
The chondrocranium at stage 23 (27-32 mm C.-R., 8 postovulatory weeks) was studied in detail to fill the descriptive gap between 7 and 9 weeks. Serial sections of ten embryos, all belonging to the same developmental stage, were investigated and compared. Graphic and Perspektomat reconstructions were made from three embryos. The chondrocranium forms a continuous mass of well-formed cartilage, which blends with early cartilage in the nasal, orbital, and otic regions, around the future foramen rotundum, and at the site of the parietal lamina. The chondrocranium and "membrane" bones cover a relatively small portion of the brain, namely 1) the medulla and pons, 2) the caudal half of the lateral portion of the cerebellar primordium, and 3) the rostroventral part of the cerebral hemispheres. The relationships of the cranial nerves were are also investigated. The degree of cranial development is intermediate between that at stage 20 (21 mm) studied by Lewis (the only other skull so far studied adequately in a staged embryo) and that of fetuses of 40 and 43 mm investigated by Macklin. On the whole, the resemblances to the fetal skulls are greater: ossification is beginning in the tectum posterius (to form the supraoccipital), and most of the "membrane" bones (except the parietal, tympanic, lacrimal, and nasal) show osseous areas. The foramen rotundum is present. The lower angle between the chordal and prechordal parts of the basal stem ranges from 129 degrees (which resembles that at stage 20, namely 122 degrees) to 115 degrees (which is the same as that at 40-43 mm). An orbito-parietal commissure is not yet present. The lower border of the larynx is at the level of the lower border of the fourth cervical vertebra. In the larynx, the thyroid laminae have usually not fused, the hyoid cartilage possesses greater and lesser cornua, the cricoid cartilage displays its signet-ring form, and the arytenoids are identifiable as condensed mesenchyme with some early cartilage. The cartilage of the first pharyngeal arches is covered in its ventral three-fourths by an osseous mandibular plate. Morphological variations within stage 23 are minor and appeared not to be related closely to each other, so that it was not possible to arrange the embryos in a linear developmental series based on their level of cranial morphogenesis.
对第23阶段（头臀长27 - 32毫米，排卵后8周）的软骨颅进行了详细研究，以填补7至9周之间的描述空白。对10个处于同一发育阶段的胚胎的连续切片进行了研究和比较。从3个胚胎制作了图形和透视重建图。软骨颅形成了一团连续的、发育良好的软骨，它与鼻、眶和耳区域的早期软骨、围绕未来的圆孔以及顶叶板的部位相融合。软骨颅和“膜性”骨覆盖了大脑相对较小的一部分，即1）延髓和脑桥，2）小脑原基外侧部分的后半部，以及3）大脑半球的嘴腹侧部分。还研究了颅神经的关系。颅骨发育程度介于Lewis研究的第20阶段（21毫米）（这是迄今为止在分期胚胎中唯一充分研究过的另一个颅骨）和Macklin研究的40毫米和43毫米胎儿之间。总体而言，与胎儿颅骨的相似性更大：后顶骨开始骨化（形成枕骨上部），并且大多数“膜性”骨（除顶骨、鼓膜、泪骨和鼻骨外）都显示出骨化区域。圆孔存在。基底干的弦部和弦前部之间的下角范围从129度（与第20阶段的122度相似）到115度（与40 - 43毫米时相同）。眶顶连合尚未出现。喉的下缘在第四颈椎下缘的水平。在喉中，甲状软骨板通常未融合，舌骨软骨有大角和小角，环状软骨呈其戒指状形态，杓状软骨可被识别为有一些早期软骨的致密间充质。第一咽弓的软骨在其四分之三的腹侧被一个骨性下颌板覆盖。第23阶段内的形态变异较小，且似乎彼此之间没有密切关系，因此不可能根据它们的颅骨形态发生水平将胚胎排列成一个线性发育系列。
