SI 6 pissection of the Eye of the Streaked Bass. 



Art. II. — Dissection of the Eye of the Streaked Bass, Perca No- 

 bilis vel Mitchelli, with Observations on the accommodation of 

 the Eye to Distances ; by W. C. Wallace, M. D., Surgeon to 

 the New York Institution for the Blind. 



The eye is of an irregular form. It is directed outwards and a 

 little forwards and upwards. It is attached to a cartilage that sur- 

 rounds the anterior part of the orbit by a conjunctiva that forms a 

 fold before it is reflected. The sclerotica is strengthened at each 

 canthus by a firm piece of cartilage ; behind, it is perforated for the 

 passage of the optic nerve ; before, the cornea which is oval is con- 

 nected in the usual way. 



Beneath the sclerotica is a layer of fat, nearly half the diameter of 

 the eye in thickness at its posterior part, but it becomes thinner as it 

 approaches the cornea where it disappears. Is this fat for retain- 

 ing the retina at a proper temperature for receiving impressions ? 



Imbedded in the fat and covered by a membrane of a tarnished 

 silver color which also surrounds the choroid is the red colored spon- 

 gy substance of the shape of a horse shoe that is peculiar to many 

 fishes, supposed by Hunter to be a muscle that alters the distance 

 of the retina from the crystalline lens, by Cuvier to be an erectile 

 tissue possessing the same influence and by others to be a gland. 

 This is easily separated into two parts as if it were cut through lon- 

 gitudinally ; the one part remaining attached to the opthalmic vessels 

 the other to the choroid coat. When quicksilver is injected by the 

 opthalmic artery it does not find its way to the choroid coat nor even 

 to the choroid portion but it well exhibits the vessels of the portion 

 connected with the artery. 



The choroid extends fi*om the part just described to the circum- 

 ference of the iris, where it appears to supply the vitreous humor and 

 where it sends vessels to the superior and inferior axes of the crys- 

 talline lens. 



The tunica ruyschiana is firm and appears to have a membrane 

 over that which secretes the pigmentum nigrum, as it does not read- 

 ily soil the fingers. 



The iris before, consists of layers of a silver color. At its cir- 

 cumference there are a number of radiated streaks. Behind, it is 

 covered with pigmentum nigrum. At its inferior portion there is a 

 loop for the passage of a muscle soon to be described. 



