摘要
蒙古绵羊胚胎发生到１４～１７ｄ（Ｅｍｂｒｙｏｇｅｎｅｓｉｓ１４～１７ｄａｙｓ，Ｅ１４～１７ｄ．）胚长１～３ｍｍ（Ｅｍｂｒｙｏｌｅｎｇｔｈ１～３ｍｍ，Ｅｌ１～３ｍｍ）。原结前方的神经板分化成神经沟，神经沟两侧的神经皱相互吻合成神经管。Ｅ１８～３０ｄ，Ｅｌ３～１５ｍｍ。神经管前段膨大成初级脑泡，进而分化成５个脑泡（即端脑胞、间脑泡、中脑泡、后脑泡及末脑泡），并显示出头曲、桥曲及颈曲。Ｅ２１～３１ｄ，神经管已分化出室管膜层、外套层、边缘层、脊神经节、脊神经及交感神经链。Ｅ１７～３０ｄ，１２对脑神经的原基逐渐发生，其中视神经及听神经发生较早，嗅神经发生较晚。Ｅ１８～３０ｄ，间脑两侧的视泡分化成视杯，视网膜原基发生。视区的外胚层又分化出晶状体及角膜。菱脑两侧的外胚层内陷形成耳泡，进而分化出内淋巴导管、椭圆囊、球囊、半规管及耳蜗的原基。Ｅ２０ｄ以后，在额鼻突的吻端，鼻板内陷形成鼻道。Ｅ２９ｄ，鼻道背侧的间充质内开始出现嗅神经纤维的原基。
The embryogenesis 14￣17 days (E14￣17d),the neural plate at the anterior region of the primitive node differentiates into the nearal groove,the nearal folds at the side of nearal groove meet to produce the neural tube. E18￣30d,the primary vesicles of local dilation of the anterior region of neural tube convert into the five vesicles(telencephalon,diencephalon,mesencephalon,metencephalon and mylencephalon),and to show the cranial,the pontine and the cervical flexure. E21￣30d,the neural tube differentiates the ependymal,the mantle and the marginal layer,the spinal and the sympathetic ganglion. E17￣30d,the rudimentes of 12 pair cranial nerves develop gradually,in which the optic and the acoustic develop early than the olfactory. E18￣30d,the optic vesicles of the diencephalic sides convert into the optic cup,the rudiment of the retina arises.The ectoderms of the optic region form further the lens and the cornea. Meantime at the rhombencephalic sides,the ectoderms invaginate to form the oticvesicle,and to differentiate further the endolymphatic duct,the utricle,the saccule,the semicircular canal and the cochlea. After E20d,at the anterior end of the frontal.Nasal process,the nasal placodes invaginate to form the nasal canal,E29d,in the mesenchyme of the nasal dorsal region begins to arise the olfactory fibrillar rudimentes.
