ORIGIN OP THE TRABECUL/E OP THE OPTIO NERVE. 491 



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and its relation to the Optic Stalk," 'Jouru. Anat. and Physiology,' 

 vol. XXX, April, 1896. 



8. E.YDER, J. A. — " Development of the Eye," ' System of Diseases of the 



Eye,' Norris and Oliver, vol. i, London and Philadelphia, 1897. 



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EXPLANATION OF PLATES 26 and 27, 



Illustrating Mr. J. T. Gradon's paper, " Researches on the 

 Origin and Development of the Epiblastic Trabeculee 

 and the Pial Sheath of the Optic Nerve of the Frog." 



Alphabetical List of Reference Letters for all the Figures. 



Br. Brain, c.c. Cartilage of the cranium, ex. Connective tissue cells 

 between the ophthalmic artery and the optic nerve, e. Eye. e. Outline of 

 pigmented epithelium of retina, e.m. Membrana limitans externa, i.m. Mem- 

 brana limitans interna, /.Lymph-corpuscle. /.<?. Lymph channel. /.*. Lumen 

 of optic stalk, m.a. Mesoblast of the arachnoid sheath, n.f. Optic nerve 

 fibres, n.s. Space occupied by nerve fibres, not represented, o.n.c. Interior 

 capillary of optic nerve, p.c. Capillary of pial sheath, p.p. Pigmented 

 protoplasm, p.s. Pial sheath, sa.s. Subarachnoid space, ir.l. longitudinal, 

 tr.o. oblique, tr.t. transverse trabeculaj. y. Granules of food-yolk. 



Fixing agent : Aceto-corr. subl. Stain : Borax carmine + picro-indigo- 

 carm. 



All the figures have been drawn with the Abbe camera. 



The terms transverse and longitudinal apply to the optic stalk. 



Figs. 1 to 8 are transverse sections taken from tadpoles, the lengths of 

 which are given below. 



They are all taken from the distal fourth of the stalk, except Fig. 2, which 

 is taken from the proximal fourth. 



They show the gradual formation of the transverse trabeeulse and the pial 

 sheath. 



The nerve fibres have only been represented in some of the figures, but they 

 will be understood to occupy the spaces between the trabecula;. 



