In most cases this cornea is divided into lenticular facets corresponding to the underlying ommatidia.
In the common species of Chiton and many others of the family Chitonidae the megalaesthetes are developed into definite eyes, the most complicated of which have retina, pigment within the eye, cornea and crystalline lens (intra-pigmental eyes) (fig.
When the trigeminus nerve is divided (Majendie), or when its root is compressed injuriously, say Iby a tubercular tumour, the cornea begins to show points of ulceration, which, increasing in area, may bring about total disintegration of the eyeball.
The ectoderm continued over the optic vesicle forms a transparent cornea (fig.
The eye is always a closed vesicle, and the internal cornea is extensive.