446 SLONAKER. [Vol. XIII. 



liest investigations till about 1830, or previous to the common 

 use of the microscope; (2) from the use of the microscope till 

 1887, or a period when the old methods of hardening and 

 staining were employed, which made only the nuclei and larger 

 processes visible; and (3) from 1887 to the present time, or 

 since the use of the silver chromate and the methyl-blue methods 

 of staining, which make clear not only the cells, but the finest 

 processes of both neurites and dendrites. 



Although Francesco Buzzi {3) is given the credit of having 

 discovered the yellow spot in the human eye in 1782, it was 

 not until 1791 that the fovea centralis was noticed. This dis- 

 covery was made by the celebrated German anatomist, Sm. Th. 

 V. Soemmerring (2), and was called for a number of years the 

 " Foramen of Soemmerring," he having considered it a per- 

 foration. Buzzi, on the contrary, thought it merely a thin and 

 transparent part of the retina. Michaelis (4) favored Buzzi's 

 theory, while Reil (5), Meckel (6), and Home (7) considered it 

 a foramen. 



The discovery of the foramen of Soemmerring in man natu- 

 rally led to many investigations in other classes of vertebrates. 

 Michaelis examined the eyes of the dog, swine, and calf, but 

 found no trace of a fovea. Home (7), however, was more for- 

 tunate. Knowing the great similarity which existed in the 

 anatomy of man and the monkey family, he wisely chose one of 

 the latter, and consequently was the first to discover the fovea 

 in the ape in 1798. He considered it a real foramen for the 

 passage of a lymphatic vessel, and tried to correlate it with 

 such a vessel in the optic nerve of the sheep and calf. Cuvier 

 (8) confirmed the presence of the fovea in the ape family, but 

 he considered it a thinning of the retina. This view gained 

 ground, but it was not firmly established till 1830, when v. 

 Ammon (9) demonstrated by the aid of the microscope that the 

 retina was continuous through the fovea. 



Albers (10) found in 1808 "a central hole surrounded by a 

 yellow border " in the giant tortoise (Testudo mydas), but was 

 not able to confirm such an appearance in the second eye. 



Knox (11) in 1823 was the first to demonstrate the presence 

 of a fovea in animals other than the primates. He examined 



