THE RETINA 657 



Most anatomists recognize ten layers in the retina: 



1. Inner limitary membrane. 6. Outer molecular layer. 



2. Expansion of fibres of the 7. Outer nuclear layer. 



optic nerve. 8. Outer limitary membrane. 



3. Layer of ganglion-cells. 9. Layer of rods and cones. 



4. Inner molecular layer. 10. Layer of pigment-cells. 



5. Inner nuclear layer. 



1. The inner limitary membrane is a delicate structure, with fine striae 

 and nuclei, composed of connective-tissue elements. It is about ^'SWQ'Q 

 of an inch (i /JL) in thickness. From this membrane, connective-tissue 

 elements (fibres of Miiller) are sent into the various layers of the retina, 

 where they form a framework for the support of the other structures. 



2. The layer formed by the expansion of the optic nerve is composed 

 of pale transparent nerve-fibres, ^Wo to 251JFO f an mc ^ (-5 to l A 6 ) 

 in diameter. These do not require special description. 



3. The layer of ganglion-cells is composed of multipolar nerve-cells, 

 measuring g^Vo" to ylro ^ an mc ^ (^ to 3 2 /*) ^ n diameter. In the centre 

 of the retina, at the macula lutea, the cells present eight layers, and they 

 diminish to a single layer near the periphery. The smaller cells are 

 situated near the centre, and the larger, near the periphery. Each cell 

 sends off several filaments (two to twenty-five), probably going to the 

 layer of rods and cones, and a single filament which becomes continuous 

 with one of the filaments of the optic nerve. 



4. The inner molecular layer consists of a plexus of minute fibrils 

 and fine granules. 



5. The inner nuclear layer is composed of nuclear bodies, rather 

 large and some of them stellate in form. 



6. The outer molecular layer consists of a plexus of fine fibrils and 

 nuclei. 



7. The outer nuclear layer presents clear, oval, nuclear bodies, con- 

 nected with the rods and cones by one process to each rod or cone, and 

 sending fibrils to the adjacent molecular layer. 



8. The outer limitary membrane is composed of delicate connective- 

 tissue elements. 



9. The layer of rods and cones is the most important of all and will 

 receive special description. 



10. The layer of pigment-cells has already been described in con- 

 nection with the choroid coat. 



Layer of Rods and Cones (Jacob's Membrane the Bacillar Membrane}. 

 -The layer of rods and cones is composed of rods, or cylinders, ex- 

 tending through its entire thickness, closely packed, and giving to the 



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