UNSW Embryology

A3: Overview of embryo (stage 22) head region where high power sections are from in A4, A5, and A6. On left of image the optic nerve can be seen projecting back to the region of the chiasm.

A4: Optic ventricle (artefactually enlarged). Optic nerve. Sensory retina. Pigment epithelium. Choroid and sclera (not separable).

A5: Top of image shows sensory retina with optic nerve fibre layer and young retinal ganglion cells. Space in middle of image is optic ventricle beneath which is the pigment epithelium (black spots). Bottom of image sclera plus choroid.

A6: Anterior corneal epithelium and posterior corneal endothelium. Corneal stroma. Angle of anterior chamber with developing trabecular meshwork. Anterior and posterior lens epithelium. Note change in height of lens cells at the equator of the lens. Double-layered epithelium of iris arising from rim of optic cup. Stroma of iris lies anteriorly across lens. Kink in internal wall of optic cup indicates site where the ciliary body will form.

B3: Overview of embryo (stage 22) head region where high power sections are from in B5 and B6. On the right of image can be seen the cartilage of the auricle (pinna) of the ear. Note the level for the external, middle and inner ear corresponds to the oral cavity (top of image).

Mesenchyme (cartilage) surrounding inner ear will ossify to form the petrous part of temporal bone.

B5: Cochlear duct. Spiral ganglion. Tubotympanic recess (auditory tube). Internal carotid artery. Malleus and incus. Meckel's cartilage. Tensor tympani muscle. Crista ampullaris of a semicircular duct. Semicircular duct. Utricle with macula. Saccule (cut tangentially) adjacent to utricle. Otic capsule.

B6: Turns of cochlea duct. Note changes in height of the wedge-shaped epithelial cells at different sites in wall of cochlear duct; the region of tallest cells is the anlage of Corti's organ and the clear luminal cytoplasm is the origin of the tectorial membrane; the thickening on the outer wall of the cochlear duct is the origin of the stria vascularis; the thinnest part of the wall is the origin of the vestibular membrane. Spiral ganglion in modiolus. Vestibular ganglion (collectively VIII cranial nerve ganglion - both parts composed of bipolar neurones). Saccule. At bottom of image can be seen the internal auditory meatus (space) between parts of temporal cartilage.