THE RETINA 25 



out. Whereas the Golgi method was employed by Tartuferi 

 (1887), and Dogiel (1888), we are indebted largely to the 

 famous Spanish neurologist, Ramon y Cajal (1893, 1894) for 

 unraveling the complexities of the finer nervous connections 

 of the retina. 



Franz (1913) published composite figures of the retinal 

 neurones in the different classes of vertebrates. These were 

 based upon the findings of earlier investigators (Retzius, 

 Neumayer, Schiefferdecker, Schafer, H. Miiller, M. Schutze, 

 Aichel, Greeff, Krause, and especially Cajal). His plates 

 have been redrawn wdth some modifications and are repro- 

 duced in Figures 17-22. These show the various types of 

 bipolar, amacrine, horizontal, gangUon, and supporting 

 cells. One important fact among others will be noted, viz., 

 that in selachians, amphibians, reptiles, and diurnal birds, 

 the rods, like the cones, make dendritic connections with the 

 bipolar cells, whereas in teleosts, nocturnal birds, and 

 mammals they end in knobs. This does not agree with 

 Putter's (1912) contention that rods and cones can be dif- 

 ferentiated by their mode of connections with the bipolar 

 cells. He claims that rods have centripetal molecular endings 

 and the cones dendritic endings. If this were true, then what 

 Franz has labeled ^'rods " in selachians, amphibians, and birds 

 would have to be considered as cones — a fact which is not 

 supported from other anatomical and physiological evidence. 



Just lateral to the posterior pole and in the line of the 

 visual axis, the retina in man, anthropoids, and some other 

 forms undergoes a localized modification of its layers to 

 form a funnel-shaped depression. In this area, which in man 

 is termed the macula lutea because of its yellow pigment, the 

 inner layers of the retina are spread apart, leaving in the 

 center a small pit, called the fovea centralis (Figure 23). In 

 this region there are no rods and the retina is characterized 

 by the presence of long slender closely packed cones. It is 

 the region of highest visual acuity and serves the function 

 of central vision. For the human eye, Duke-Elder describes 

 three regions as follows : 



