. Quain's elements of anatomy . appear to enclose it, but leaves THE OEGANS OF SEXSE: THE EYE. 843 for a time an aperture or depression below. This is the choroidalfold or fissure, which may easily be distinguished in the embryo-headafter pigment has been deposited, from the circumstance that the pig-ment is absent from the cleft, which thus appears for a time as a broadwhite line, particularly ob^aous in the embryo bird, running from thecircumference in upon the lens. Fig. 750.—Diagrammatic sketch op a VERTICAL LONGITUDINAL SECTION THROUGIITHE EYEBALL OF A HUMAN FOETUS OF FOUR WEEKS. (After K
. Quain's elements of anatomy . appear to enclose it, but leaves THE OEGANS OF SEXSE: THE EYE. 843 for a time an aperture or depression below. This is the choroidalfold or fissure, which may easily be distinguished in the embryo-headafter pigment has been deposited, from the circumstance that the pig-ment is absent from the cleft, which thus appears for a time as a broadwhite line, particularly ob^aous in the embryo bird, running from thecircumference in upon the lens. Fig. 750.—Diagrammatic sketch op a VERTICAL LONGITUDINAL SECTION THROUGIITHE EYEBALL OF A HUMAN FOETUS OF FOUR WEEKS. (After KoUiker.) ^{. The section is a little to the side so as toavoid passing through the ocular cleft, c,the cuticle, where it later covers thecornea; Z, the lens ; op, optic nervefoi-med by the pedicle of the primary opticvesicle; vp, primary medullary cavity ofthe optic vesicle ; p, the pigment-layer ofthe outer-wall; r, the inner wall form-ing the retina; vs, secondary optic vesiclecontaining the rudiment of the % The lens is developed in the part of the cuticle opposite to the mostprojecting part of the primary optic yesicle, or at the place where thisvesicle comes in contact with the surface of the head. In this situationthere is seen from a very early period a thickening of the epiblast, Avhichseems to reside chiefly in its deeper layer of cells, and in birds andmammals it would appear that an actual involution of the cuticle takes Fig. 751.—HORIZONTAL SECTION THROUGH THE ETKOP AN EMBRYO RABBIT OP TWELVE DAYS AND SIX HOURS, f. (From Kolliker.) 0, stalk of the ocular vesicle with wide cavity ; h,remains of the cavity of the primitive ocular vesicle ;p, proximal lamella of the secondary vesicle (pig-mentum nigi-um) ; r, distal lamella (retina) ; g,vitreous body; I, lens vesicle, widely open at ol;I, papillar elevation in the bottom of the lens vesiclewhich forms the lens ; m, with v, an annular vesselat the anterior border of the secondarj vesicle ; e,epiblast.
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Keywords: ., boo, bookcentury1800, booksubjectanatomy, booksubjecthumananatomy
