DISEASES OF THE RETINA AND CHORIOID 127 



examination will teach one the difference. The tape turn 

 lucidum may also be mistaken for a pathologic lesion. 

 The brilliancy and varied coloring of this portion of the 

 fundus is most interesting. A fowl's fundus distinctly 

 differs from a quadruped's. There is a projection into 

 the vitreous, known as the ^'pecten," said by some 

 authors to be a projection of the chorioid, and by others 

 to be a portion of the retinal circulation. It appears on 

 cross-section of the eye to project from the optic nerve. 



The retina, although histologically divided into ten 

 layers, may properly be divided into tissues of two 

 kinds— a nervous and a supporting tissue. It is said to 

 be transparent, which is quite evident in fundi with 

 little or no pigment when the outlines of the vessels of the 

 chorioid can be seen through it. Its system of blood- 

 vessels is particularly its own, as they do not anastomose 

 with themselves or other systems of vessels except at the 

 papilla, where there is a minute connection between the 

 retinal and ciHary vessels. 



The retina is subject to anemia, edema, hyperemia, 

 hemorrhages, detachment, inflammation, and atrophy. 



Anemia occurs with general anemia and follows severe 

 hemorrhages from other portions of the body. It also 

 occurs in compression and embolism of the central 

 artery. There is a reduction in the cahber of the vessels 

 and the retina is generally pale. 



Edema is the result of traumatism and disease, and is 

 due to effusion in the retinal tissues. It presents a 



