602 



TEXT-BOOK OF PHYSIOLOGY. 



In the posterior portion of the retina, at a point corresponding 

 with the axis of vision, there is a small oval area about 2 mm. in 

 its transverse and about 0.8 mm. in its vertical diameter. From the 



fact that it becomes 



Pigment-layer (not shown). yellow after death, it is 



known as the macula 

 lutea. This area pre- 

 sents in its center a 

 depression with slop- 

 ing sides, known as 

 the jovea centralis. 

 About 3.5 mm. to the 

 nasal side of the 

 ma.cula is the point of 

 entrance of the optic 

 nerve. 



The retina is re- 

 markably complex in 

 structure, presenting 

 an appearance when 

 viewed microscopic- 

 ally, something like 

 that represented in 

 Fig. 279, indicating 

 that it is composed of 

 different cellular ele- 

 These have been named, from behind 



2. Layer of rods and cones. 



3. External limiting membrane. 



4. Outer nuclear layer. 



5. Outer molecular layer. 



6. Inner nuclear layer. 



7. Inner molecular layer. 



8. Layer of ganglion cells. 



9. Layer of nerve-fibers. 



FIG. 279. VERTICAL SECTION OF HUMAN RETINA 

 (Schaper.) 



layers. 



ments arranged in 

 forward, as follows : 



1. The layer of pigment cells. 



2. The layer of rods and cones, or Jacobson's layer. 



3. The external limiting membrane. 



4. The outer nuclear or granular layer. 



5. The outer molecular or reticular layer. 



6. The inner nuclear or granular layer. 



7. The inner molecular or reticular layer. 



8. The layer of ganglion cells. 



9. The layer of nerve-fibers. 



Modern histologic methods of research have made it possible to 

 reduce the retina, exclusive of the pigment cells, to three successive 

 layers of nerve-cells, supported by a highly developed neuroglia, 

 forming what has been termed the fibers of Miiller. These nerve- 

 cells are as follows : 



i. The visual cells. 

 * 2. The bipolar cells. 



3. The ganglion cells. 



