Chapter IV 



A REVIEW OF THE ANATOMY AND PHYSIOLOGY OF THE 



ORGANS AND TISSUES SEEN IN THE FUNDUS 



OCULI OF THE BIRD 



A comparison of the ocular structures in the 

 vertebrate sub-classes shows that the posterior 

 two-thirds of the eyeball contain practically 

 the same organs in all, with, of course, numer- 

 ous modifications of them to suit the visual 

 requirements of a particular species. 



In Vertebrates generally the fundus organs 

 of especial interest are the retinal and choroidal 

 bloodvessels (in some instances projected into 

 the vitreous humor), the choroid, the retina 

 and the optic nerve entrance, the last named 

 otherwise known as the optic disc, porus 

 opticus, nerve-head or papilla. 



Although the retinal layers are generally 

 transparent, and not visible during life, yet 

 this is not true of all species; e.g., occasionally 

 a certain number of translucent nerve-fibre 

 sheaths (neurilemmata) are prolonged into 

 the retina and variously distributed over the 

 background of the eye, and, by means of the 

 ophthalmoscope especially, are visible and 

 have been described under the name medul- 

 lated or "opaque" nerve fibres. 



These organs and tissues will be considered 

 in their order. 



Fig. 1 



The Relations of the Fundus Organs of a Young 

 English Sparrow. A, area centralis; F, fovea; O, optic 

 nerve entrance; P, pecten. The pecten stands almost 

 vertical in this figure. (Wood and Slonaker.) 



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