432 % SPOT OF SOEMMERING. 



plaits of the retina about this place; one of these, which is 

 very constant, extends from the optic nerve to this spot. 



The color of this spot is pale in children, bright in young 

 persons of mature age, and pale at an advanced period of 

 life. 



The foramen is to be found in the foetus, but not the yellow 

 spot. The color of the spot diminishes when vision is obstruct- 

 ed ; and the spot disappears when vision is lost. 



Fig. 193.* 



There is the greatest reason to believe that the retina is the 

 seat of vision ; but it has been ascertained, most decisively, 

 that the extremity of the optic nerve, from which the retina 

 originates, is insensible to the rays of light. 



Professor Knox of Edinburg, and J. Dalrymple, from 

 many careful observations made upon the subject, consider 

 the folds of Soemrnering, as entirely a post mortem appearance, 

 dependant on a collapsing of the retina, consequent to the 

 escape of the fluids through the cornea, which takes place 

 speedily after death. This corresponds with my own observa- 



* Fig. 193 represents the retina, to which the optic nerve is attached behind, 

 expanded in the form of an incomplete sphere over the hyaloid membrane of 

 the vitreous humor, and terminating in front a short distance from the lens. 

 The lens is seen lodged with its capsule, in a depression on the front of the 

 vitreous humor, and surrounded by a series of delicate folds, (zona ciliaris,) 

 which correspond with the ciliary folds of the choroid, (see fig. 191.) The spot 

 of Soemmering is seen near the entrance of the optic nerve. P. 



