PLATE 3 



EXPLANATION OF FIGURES 



Microphotographs of sections through the eye of a young sparrow just after 

 it had made its first trial flight, about twelve or fourteen days after hatching. 

 A, area centralis; Ap, annular pad of lens; Br, brain; C, cornea; Ca, thickened 

 portion of scleral cartilage surrounding the optic nerve entrance; Ch, chorioid; 

 Cm, ciliary muscles; Cp, ciliary processes; F, fovea; Hg, Harder 's gland; I, iris; 

 L, lenticular portion of lens; Lc, lenticular chamber; LI, lower lid; Lu, upper 

 lid; M, eye muscles; Ml, muscle of lower lid; A'', nictitating membrane; Op 

 N, optic nerve; Or, ora serrata; P, pecten; Pm, free margin of pecten showing 

 how the folds are united into a median ridge; Ptj, pyramidalis; Q, quadratus 

 muscle; Sc P, scleral plates; T, tendon from pyramidalis muscle. 



10 Horizontal section of left eye of young about fourteen days after hatch- 

 ing, section passes through the center of the fovea but to one side of the center 

 of the lens. The fovea, F, shows a marked depression. X 10. 



11 Same series as fig. 10 passing through the area centralis. A, at the edge 

 of the fovea. X 10. 



12 Same series as fig. 10 passing through the center of the lens. The lens 

 appears as the typical adult lens. The breaks and spaces, except the lenticular 

 chamber, Lc, are due to hardening and are not normal. The pyramidalis (Pij) 

 with its tendon (T) passing through the loop of the quadratus muscle (Q) is seen. 

 X 10. 



13 Same series as fig. 10 at a lower level some distance below the proximal 

 portion of the nerve entrance. The free margin of the pecten (Pm) shows how 

 the folds merge into a single median densely pigmented mass. The tendon, T, 

 of the pyramidalis muscle is seen surrounded by the sheath-like loop of the 

 quadratus. X 10. 



14 Vertical section of the right eye of the same bird as fig. 10. Section 

 passes through the center of the lens and the distal end of the pecten .030 mm. 

 beyond the last trace of the optic nerve. The anterior part of the lens from 

 which the annular pad is derived appears as a mere line. The ciliary processes 

 are closely attached to the lens. The ciliary muscles, Cm, appear as a dark area 

 lying just inside the scleral plates, Sc P. The muscle of the lower lid. Ml, can be 

 traced back to the posterior part of the eye socket where it is closely attached 

 to the orbital side of the inferior rectus muscle. X 10. 



15 Same series as fig. 10, showing the place where the most distal part of the 

 optic nerve penetrates the retina. X 10. 



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