ORGANS 



ID THE COMMON INTEGUMENT 



As the nerve fibers pass through the lamina cribrosa sclerse they lose their medullary sheaths 

 and are continued onward through the choroid and retina as simple axis-cylinders. When they 

 reach the internal surface of the retina they radiate from their point of entrance over this sur- 

 face grouped in bundles, and in many places arranged in plexuses. Most of the fibers are 

 centripetal, and are the direct continuations of the axis-cylinder processes of the cells of the 



ganglionic layer, but a few of them 

 Membrana limitans 



^, interna 



-Stratum opticum 



.Ganglionic layer 





Fibers of Muller 



are centrifugal and ramify in the 

 inner plexiform and inner nuclear 

 layers, where they end in enlarged 

 extremities. 



2. The ganglionic layer consists 

 of a single layer of large ganglion 

 cells, except in the macula lutea, 

 where there are several strata. The 

 cells are somewhat flask-shaped; the 

 rounded internal surface of each 

 resting on the stratum opticum, and 

 sending off an axon which is pro- 

 longed into it. From the opposite 

 end numerous dendrites extend into 

 the inner plexiform layer, where 

 they branch and form flattened 

 arborizations at different levels. 

 The ganglion cells vary much in 



size, and the dendrites of the smaller ones as a rule arborize in the inner plexiform layer as soon 

 as they enter it; while those of the larger cells ramify close to the inner nuclear layer. 



3. The inner plexiform layer is made up of a dense reticulum of minute fibrils formed by the 

 interlacement of the dendrites of the ganglion cells with those of the cells of the inner nuclear 

 layer; within this reticulum a few branched spongioblasts are sometimes imbedded. 



Membrana 

 limitans interna 

 Stratum opticum,'" 



Ganglionic layer -- 



FIG. 881. Section of retina. 



i Inner plexiform layer 



Inner nuclear layer 

 Outer plexiform layei 



Outer nuclear layer 

 Membrana limitans 



externa 

 Layer of rods and 



cones 



Pigmented layer 

 (Magnified.) 



Inner 'plexiform 

 layer 



Centrifugal fbre * 



Inner nuclear 

 layer 



Fibre of Mailer- 

 Outer plexiform .. 

 layer 



Outer nuclear _ 

 layer 



Membrana 

 limitans externa, 



Layer of rods 

 and cones 



'"" Diffuse amacrine 

 cell 



'.Amacrine cells 



1 o 1 o I o I o 1 o I 



FIG. 882. Plan of retinal neurons. (After Cajal.) 



4. The inner nuclear layer or layer of inner granules is made up of a number of closely packed 

 cells, of which there are three varieties, viz.: bipolar cells, horizontal cells, and amacrine cells. 



The bipolar cells, by far the most numerous, are round or oval in shape, and each is prolonged 

 into an inner and an outer process. They are divisible into rod bipolars and cone bipolars. The 



