286 THE RETINA, BY MAX SCHULTZE. 



cone and rod fibres, such as they pursue in other parts of the 

 human retina, and in the retina of animals that do not possess 

 a fovea cent-rails, is re-established. An oblique direction, as 

 Hulke has observed, is pursued also by the nerve fibres of the 

 internal granule layer. In transverse sections carried through 

 the macula lutea and fovea centralis, I found that the rod 

 and cone fibres pursue an oblique course outwards on every 

 side from the fovea for two millimeters in the horizontal meri- 

 dian, but only for about 1*5 millimeters in the vertical meri- 

 dian. According to Hud. Schirmer^s observations on the oph- 

 thalmoscopic appearance of the macula lutea in healthy eyes, it 

 is always of a tranversely oval form ; its horizontal in relation 

 to its vertical diameter being as 4 : 3.* The ganglion cells of 

 the yellow spot are for the most part bipolar, as has been 

 stated by various observers, and recently by Merkel. 



The connective substance at the yellow spot, as has been 

 already mentioned, is particularly tender and delicate, and has 

 no thick radial supporting fibres. On the other hand, the 

 membrana limitans interna becomes quite thick and strong. 

 According to Merkel, it attains a thickness of three micro- 

 millimeters, though it again becomes attenuated at the fovea 

 centralis. It separates with extraordinary facility from the deli- 

 cate spongy connective tissue that occupies the interspaces 

 between the ganglion cells. 



A macula lutea and fovea centralis are only present in Quaclrumana 

 amongst Mammals, but here entirely agree in their anatomical charac- 

 ters with the corresponding parts in Man. Kernak and H. Miiller^: have 

 pointed out the existence of an area centralis, with a structure similar 

 to the yellow spot in the retina of several Mammals ; but we possess 

 no precise information on the point. That in the retina of some 

 Birds, not only one, but two fossae are present at some distance from 

 each other, was discovered by H. Miiller, though he gave no details 

 in regard to the principal elements of these parts. According to my 



* Grafe, Archiv, Band x., 1, p. 150. 



f Max Schultze, Sitzungsberichte der Nieder-rheinische Gesellschaft zu 

 Bonn, Juli, 1861. 



$ Wurzburg naturwiss. Zeitschrift, Band ii., p. 140, 1861. 



Loc. tit., and in his- treatise Ueber das Auge des Chamaleon, p. 11. 



