VISUAL TISSUES 



247 



torial region, leaving a somewhat thinner and very transparent pole of 

 the eye for the light-rays to come through. In the corneal cells the 

 nucleus is placed somewhat higher. 



The place inside of this outer covering contains the remaining organs 

 of the eye in the following order from distal to proximal positions. A 

 lens, a blood sinus, the several layers of the retina, a space filled with a 

 vitreous humor, the argentea, and the pigmented tapetum. These all 

 lie in an oval space, the eye-sac, and a nerve approaches this sac through 



FlG. 219. Eye of Pecten irradians. cor., cornea; /., lens; bl.s., blood sinus; o.gn.c., outer 

 ganglion cells upon which lies a layer of supplying nerve fibers; vis.c., visual cells; lim.m., 

 limiting membrane; vis.r., visual rods; ar., argentea; tap., tapetum; nv.f., nerve fiber. 

 (After PATTEN.) 



the proximal connective tissue and divides into two branches, a basal 

 branch and a lateral branch. 



The lens is unlike so many of the lenses we have previously examined, 

 in that it is composed of a mass of cell bodies instead of secreted cell- 

 products. These cells have round nuclei of moderate size, and are nearly 

 fitted together to form a round body with curved surfaces coming to a 

 sharp, circular edge. This body lies directly against the cornea whose 

 proximal surface is in contact with its distal surface, and its edges reach 

 as far as the pigment area of the cornea or iris. Its proximal curve, 

 projecting into the blood space, almost touches the next organ, which is 

 the retina (Fig. 219). 



This retina is a thick mass of tissue inclosed in a separate membrane 



