360 ANNUAL OF SCIENTIFIC DISCOVERY. 



of her mouth, in so far as it is abnormal, is more likely the result of disease 

 than a character of a tribe. The causes of these peculiarities must be sought 

 for among those which modify the products 'of conception and impress various 

 fancied or real animal or vegetable resemblances upon the foetus in utero ; and 

 which, in some inexplicable way, seem to arrest or modify animal develop- 

 ment. 



THE HUMAN RETINA. 



In a memoir read before the Academy of Sciences, September 26, 1854, by 

 Kolliker and H. Muller, they announce some important investigations relative 

 to the structure, the connection, and the probable function of the different 

 parts of the retina. They describe the following layers : 1. Rods and cones. 

 2. Nucleiform bodies. 3. Gray substance. 4. Expansion of the optic nerve. 

 5. Limiting membrane. Passing over the last, it has been discovered by 

 Kolliker that the expansion of the optic nerve is interrupted at' the macula 

 lutea, which exhibits no trace of nerve-fibers, while the nerve-cells form there 

 a very thick layer of 9 to 12 superimposed rows. In other parts the termina- 

 tion of the nerve-fibers of the retina directly in the nerve-cells has been 

 fully confirmed, the fibers becoming continuous with the processes, 1 to 6 

 in number, which these cells present, resembling entirely the prolongations 

 of the ganglionic corpuscles of the brain and nervous ganglia. The nerve-fibers 

 may, therefore, be said to originate from the nerve-cells. The cones (hitherto 

 imperfectly described) are thicker and shorter than the rods, on the inner part 

 of which they are placed ; they present externally a prolongation resembling 

 a short rod ; they are pretty regularly set, and at the macula lutea, where the 

 rods are entirety wanting, the cones are abundant and form a continuous 

 layer. From the internal part of each cone and rod there proceeds a fiber 

 which passes through all the layers of the retina, and becomes lost on the 

 inner surface of the limiting membrane. These fibers, first observed by H. 

 Muller in animals, are in relation with the nucleiform bodies ; they have been 

 named " fibres radiares," and are probably of great importance in regard to 

 the functions of the retina. 



From their observations the authors conclude that the nerve-fibers of the 

 retina do not serve for the objective perception of light, because they are de- 

 ficient at the macula lutea, where vision is acute, and because the optic nerve 

 itself is insensible of luminous impressions. It is improbable that the nerve- 

 cells, or nucleiform bodies which exist in several superimposed rows, can give 

 rise to any very exact visual impression. The cones and rods remain, there- 

 fore, as the most likely parts to receive the impression of light, of which the 

 Mosaic-like disposition would render the sensation as definite and exact as 

 possible. The authors, however, have not completely demonstrated the con- 

 nection by which such impressions could be transmitted to the fibers of the 

 optic nerve; but they suppose that this communication takes place, 1st, by 

 means of the radiary fibers, which connect the cones with the nucleiform 

 bodies. 2d. By means of the processes of the nucleiform bodies, which be- 

 coming continuous with the external processes of the nerve-cells, would com- 



