2 Golding- Bird and Schäfer', 



Müller gives no figure of the fovea in man, but in another paper ^) 

 he describes and figures the structure of the same part in the chame- 

 leon and from this and the comparisons which he draws between the 

 two it is clear that he fully recognises the many points of similarity 

 which they exhibit. In the figure of the chameleon's fovea a dipping 

 inwards of the membrana limitans externa which is covered by long 

 slender cones, is distinctly represented; and the cone-nuclei are shown 

 to be here removed from the limitans externa instead of being closely 

 applied to that membrane as is the case over the rest of the retina. 



The measurements given by Müller would give the human fovea 

 the form of a small horizontally extended pit with steep sides, some- 

 what like the figures given by Hulke and Krause (see fig. 2). Henle^) 

 figures a broadly open fovea which he states to be only 0-2 mm. 

 diameter but calculated from the magnification of the figure it must 

 be at least double this. He gives the thickness in the middle as 

 about 0-1 mm. but the figure again represents it as somewhat greater 

 (0-123 mm. without the pigment layer). There is no distinct depres- 

 sion of the external limiting membrane. The retinal elements are 

 evidently so Hi-preserved as to render it extremely difficult to deter- 

 mine their relations at this part. 



Hulke ^) gives a description of the yellow spot and central fovea 

 which is in many respects different from tliat of H. Müller. He figures 

 the fovea as a deep pit with steep sides terminating in a point, oppo- 

 site the very middle of which there are no recognisable retinal elements 

 except the cones; this most central part is however quite narrow, 

 almost linear, and the retinal layers with the exception of the nerve- 

 fibre layer are all represented as extending quite up to the centre. 

 Tlie limitans externa is a plane, without any depression; the cones 

 opposite the centre of the fovea are not delineated as longer than 

 elsewhere in the macula; the cone -nuclei are absent opposite the 

 very middle of the fovea, which appears occupied below the cones 

 by a blending of the inner granules and ganglion cells. Near the 



') Würzburger naturwissenschaftliche Zeitschrift. 1862. Bd. III. 



■*) Uandbuch der system. Anatomie. ISGO. — Eiugeweidelehre. Fig. ."Jl'i. j). G02. 



'■') Phil. Trans. 1S07. 



