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EMBRYOLOGY 



MESENCEPHALON 



SENSORY LAYER 



ANTERIOR CAROINAL VEIN 



OPTIC CUP 



PIGMENT LAYER 



DORSAL AORTIC ROOT 



HYPOPHYSIS 



STOMOOEUM 



MUCOUS GLAND 



Fig. 77. A diagram of a cross section through the eyes of the embryo at about 

 stage 20. This section is just behind the optic stalk, and thus the attachment of 

 the eye with the brain is not shown. The spaces between the structures are filled 

 with loose mesenchyme. 



The thin outer layer deposits black pigment in a later stage. The optic cup 

 remains attached to the forebrain by the optic stalk, which forms the sub- 

 stratum for the growth of the optic nerve. The lens forms as a thickening of 

 the inner layer of epidermis and has a small cavity. The lens cells form lens 

 fibers, which become transparent. The epidermis over the eye also becomes 

 transparent and differentiates into part of the cornea. 



Underneath the forebrain and midbrain is the hypophysis. This group of 

 cells arose from a thickening of the head epidermis. The cells become de- 

 tached from the epidermis, and the hypophysis migrates between the pharynx 

 and the forebrain to unite with the infundibulum to form the pituitary body. 



