THE KETINA. 431 



in contact with it, and is not tinged by it. No vessels pass 

 from it to the choroides : and, when a posterior section of the 

 eye is made, it slips from it without any appearance of adhesion, 

 being attached only to the optic nerve. 



Most anatomists agree respecting these circumstances, but 

 there is the greatest difference of opinion respecting the extent 

 of the retina. Several distinguished anatomists, of the last 

 century, thought very differently from each other on this sub- 

 ject ; and two of the first anatomists of the present day have 

 embraced opinions entirely opposite. Monro is convinced 

 that it extends under the ciliary processes, to the crystalline 

 lens: and Soemmering asserts, positively, that it terminates at 

 the commencement of the ciliary processes.* Some of the 

 anatomistsf of London incline to the opinion embraced by 

 Soemmering; and the late ingenious Bichat adopted the opinion 

 embraced by Monro. 



Both parties confide in their own observations, and refer to 

 the eye. An object which appears so very different to different 

 persons, who have good sight, cannot be very distinct. The 

 pulpy substance of the retina appears to terminate at the com- 

 mencement of the ciliary processes ; but a membrane of a 

 very different texture seems continued from it to the crystal- 

 line lens. 



Although the eye and the retina have long been objects of 

 anatomical attention. Professor Soemmering made an inter- 

 esting discovery respecting it, so lately as the year 1791, viz. 

 that, at the posterior part of the retina, on the axis of the eye, 

 and, of course, a little exterior to the entrance of the optic 

 nerve, there is a spot of a circular or oval figure, about one 

 line, or rather more, in diameter, of a yellowish or saffron 

 color, which is brightest about the centre. 



In the centre of this spot is a round hole, equal in diameter 

 to one-fourth of the spot. There are, generally, several small 



♦ This opinion of Soemmering, which was advocated by Zinn and Mor- 

 gagni, and more recently by MecJjel, is now generally admitted. By careful 

 observation it may be seen terminating a short distance behind the ciliary 

 body. — p. 



•f- See the new CyclopEedia, by Dr. Reese and others, article eye. 



