|WikiProject Anatomy||(Rated Start-class, Mid-importance)|
Corrected VERSION of the DEVELOPMENT of the EYE
The development of the fertilized ovum reaches first the stage of the embryo formed by two layers: the ectoderm and the endoderm.The ectoderm gives rise to the mesoderm which inserts itself between the ectoderm and the endoderm. Then the embryo appears formed by its three main germinal layers: the ectoderm, the mesoderm and the endoderm. The eye structures derive from the ectoderm and the mesoderm. The ectoderm invaginates forming the neural groove; on both sides of the groove, the ectoderm raises up to form the neural folds which after fusion give rise to the NEURAL CANAL. The invaginated cells of the ectoderm which have formed the neural canal become the NEURAL ECTODERM. The neural ectoderm is the anlage of the Nervous system and the EYE. The remaining ectoderm becomes the SURFACE ECTODERM. As to the MESODERM, it arranges itself along both sides of the neural canal and form the somites. It constitutes the PRIMARY MESODERM.The anterior portion of the neural canal enlarges and forms the brain and the eye. The surface ectodermal cells located above the neural canal proliferate, migrate sideways and form the NEURAL CREST CELLS. These neural crest cells mix up with the primary mesodermal cells to form the SECONDARY MESODERM. This mesoderm will form most of the mesenchymal elements of the eye. The anterior portion of the neural tube develop into a hollow structure presenting three enlargements separated by two constrictions. These are the PRIMARY BRAIN VESICLES: the forebrain (Prosencephalon), the midbrain (Mesencephalon) and the hindbrain (Rhombenephalon).An anterior flexion appears between the midbrain and the hindbrain portions of the enlarged anterior portion of the neural tube; this is called the CEPHALIC FLEXURE.
SULCUS or OPTIC PIT, appears on the inner side of the midbain, on both sides of the midline. This optic pit evaginates, forms an OPTIC VESICLE which grows outwards towards the surface ectoderm. This is the result of closure of the neural canal, anteriorly and posteriorly, of accumulation of fluid and increase in pressure in the neural canal. When the Optic vesicle comes in contact with the surface ectoderm, the cells of of the surface ectoderm overlying the optic vesicleb start to proliferate to form the LENS PLACODE or LENS PLATE.
The Lens Plate induces the invagination of the Optic vesicle which becomes OPTIC CUP. The Lens plate changes into a LENS VESICLE which becomes inserted into the cavity of the Optic cup.
The Optic vesicle cavity was connected wih the neural tube cavity through the OPTIC STALK a short tube lined by the neuroectodermal cells which formed the optic vesicle. This connection persists after the process of invagination, between the neural tube cavity and the space present between the two layers of the optic cup. This space becomes later the subretinal space.
To the Editor I wrote my comments as a CORRECTED VERSION of the article in order to substitute the terms used in the article with the correct terminology. In Embryology each term used conveys not only the stage but also the sequence of the steps which culminate in the appearance of this stage. Anyway, your comments would be most wellcome and I would appreciate receiving clarification about what Parent Development means.