24 Golding Bird and Schäfer, 



of Hulke and Krause are much more limited in diameter and their 

 sides much steeper. Krause states regarding this point "doch erschien 

 die Grube an den Rändern der Fovea selbstverständlich weit flacher, 

 nicht mit so steilen Rändern abfallend wie in der Figur". The fovea 

 of Schultze is also steeper than ours but the difference is less marked 

 than with those previously mentioned ^). Schwalbe's figure gives nearly 

 the same curve of the internal fovea as is shown in our preparation, 

 as do also those of Henle and Cadiat, and a meridional section of the 

 fovea of a foetus of 8V2 months which is represented by Chievitz^) 

 has nearly the same general outline. The fovea of the chameleon as 

 shown by H. Müller and recently by W. Krause ^) has a very similar 

 general sectional outline to ours. 



2. As to the existence of an external fovea due to the cupjnng 

 in of the limitans externa. 



On this point the sections and photographs are explicit. The 

 cupping of the limitans externa may be even sharper and steeper than 

 that ol the limitans interna. Its centre is almost angular in section in 

 the specimen figured, tapering to a blunt point and having a sectional 

 angle of about 120'^, whereas, as we have seen, the curve of the internal 

 fovea is quite gradual. In our other specimens the curve of the outer 

 fovea is more gradual but always present and well marked. The 

 external fovea in fact so far from being absent and the result of 

 misinterpretation of the position of the outer granules, as Schwalbe in 

 the passage above quoted (p. 7) has suggested, is a most distinct 

 formation; far more so in fact in our specimen than could be supposed 

 from tlie diagrams of previous observers. Its horizontal width is not 

 much less than that of the internal fovea, viz 0-8 mm.; but the dip 

 is at first very gradual and afterwards steeper. The depth of the 

 external fovea, measured along a line passing vertically from tlie 

 middle to meet another line joining the margins of the dip, is 0-1 mm.; 



'j One of Sclmltze's original drawings gives a curve of the intenial fovea 

 very rancli like that we have rfijiresontfid (Arch. f. mikr. Anat. Bd. II. PI. XII. 

 Fig. 2). 



*) Chievitz, Inteni. Monatsschrift f. Anat. u. Physiol. 1887. Bd. IV. 



'■') W. Krause, Intern. Monutsschrift. Bd. X. 



