THE ORGANS OF SPECI.\L SENSE 



577 



per-cent. formalin. Then wash in water and bisect the eye in such a manner 

 that the knife passes through the optic-nerve entrance and the centre of the 

 cornea. The half eye should now be placed in a dish of water and the structures 

 shown in Fig. 366 identified with the naked eye or dissecting lens. On removing 

 the vitreous and retina, the pigmented epithelium of the latter usually remains 

 attached to the chorioid from which it may be scraped and examined in water or 

 mounted in glycerin. In removing the lens note the lens capsule and the sus- 

 pensory ligament. The lens may be picked to pieces with the forceps, and a 

 small piece, after further teasing with needles, examined in water or mounted 

 in glycerin or eosin-glycerin. The retinal surface of the chorioid shows the 

 iridescent membrane of Bruch. By placing a piece of the chorioid, membrane-of- 

 Bruch-sidc down, over the tip of the finger and gently scraping with a knife in 



Conjunctival epithelium ~ 



Vitreus 



Lens vesicle- h^'ig t~g:i . - - ^33 ^-:^ ^ • . ,, 



Optic stalk 



Retina (inner layer 

 of optic cup) " 



Pigmented layer of retina. _ _ 

 (outer layer of optic cup) 



Fig. 384. — Diagram of developing lens and optic cup. (Duval.) The cells of the 

 inner wall of the lens vesicle have begun to elongate to form lens fibres. The epithelium 

 over the lens is the anlage of the corneal epithelium. The mesodermal tissue between 

 the latter and the anterior wall of the lens vesicle is the anlage of the substantia propria 

 comeae. 



the direction of the larger vessels, the latter may be distinctly seen. By now 

 staining the piece lightly with hasmatoxjdin and strongly with eosin, clearing in 

 oil or origanum and mounting in balsam, the choriocapillaris and the layer of 

 straight vessels become distinctly visible with the low-power lens. In removing 

 the chorioid note the close attachment of the latter to the sclera, this being due 

 to the intimate association of the fibres of the lamina suprachorioidea and of the 

 lamina fusca. If the brown shreds attached to the inner side of the sclera be 

 examined, the pigmented connective-tissue cells of the sclera can be seen. 



(2) For the study of the finer structure of the coats of the eye, a human eye 

 if it is possible to obtain one, if not, an eye from one of the lower animals, should 

 be fixed in formalin-Muller's fluid (technic 6, p. 7) and hardened in alcohol. (A 

 few drops of strong formalin injected by means of a hypodermic needle directly 

 into the vitreous often improves the fixation.) The eye should next be divided 

 into quadrants by first carrying the knife through the middle of the cornea and of 

 the optic-nerve entrance, and then dividing each half into an anterior and a 

 posterior half. Block in celloidin, cut the following sections, and stain with 

 haematoxylin-eosin (technic i, p. 20). 



(a) Section through the sclero-corneal junction, including the ora serrata, 



I 



