1896.] Acute Visiofi in the Vertebrates. 29 



into the vitreous chamber before immersing in 70 per cent, 

 alcohol to allow the liquids to pass in. Just before putting 

 into celloidin, a window is made parallel to the plane of de- 

 sired sections, and the hardened vitreous humor is easily re- 

 moved without injury to the retina or other structures. This 

 method is now used with small eyes instead of the injection, as 

 it is so much easier of manipulation. 



In order to show the relation of the retinal arteries to the 

 area and fovea centralis, they were injected with the gelatine- 

 carmine mass of Ranvier. In small animals this injection was 

 made in the carotid arteries, while with large animals the eyes 

 were removed and the injection made into that branch of the 

 ophthalmic artery which supplies the retina. After injection, 

 the eyes were at once cooled and hardened in alcohol. When 

 hardened, the front half of the globe and the vitreous humor 

 were carefully removed, exposing to view the retina, arteries, 

 entrance of nerve, and area and fovea centralis, when present. 

 The fovea is at once seen if it be present, but the area is some- 

 times very difficult to discern, and, were it not for the blood- 

 vessels acting as land-marks, it might be overlooked altogether. 

 Drawings were made of this posterior half, great care being 

 taken to orient it, so that one would look into it along the axis 

 of vision. 



The results of these injections only serve to substantiate 

 Miiller's observation. 3 He states that mammals are the only 

 class of vertebrates which possess, in the true sense, a retinal 

 circulation, while with many mammals only a meagre circu- 

 lation is present (horse and rabbit). Fish and amphibians 

 possess a good circulation in the hyaloid membrane, while 

 birds and many reptiles have the circulation of the pecten. 

 Huschke states that these vessels of the hyaloid membrane and 

 the pecten correspond to the retinal vessels in mammals. They 

 do not, however, penetrate the retina. 



With animals which have neither retinal nor hyaloid ves- 

 , sels, it would appear that the retina is nourished by the cho- 

 roidal vessels. In fact, in animals with good retinal circula- 

 tion, the capillaries do not penetrate deeper than the outer 



S H. Muller, Anatomie und Physiologie des Auges, p. 117. 



