PRACTICUM VII. THE EYE OF THE SHKK1' 

 PLATES REQUIRED : XVI AND XIX. 



Also some figure of a section of the eye-ball, such as contained in all works on Anat- 

 omy or Physiology ; a section of the cat's eye is represented in Anatomical Technology, 

 Fig. 126. 



i. Review Pract. VI 5-7, for the location of the eye, the form of 

 the ORBIT, and the PLICA or third eyelid. 



\ 2. The following directions and descriptions refer directly to the sheep's eye ; but 

 that of the cat might be employed instead, and should be compared if possible. 



a. If possible the eyes should retain the lids for a width of 1-2 cm., and special care 

 should be taken to retain their mesal (inner or nasal) junction ; if the lids have been 

 removed the directions in '$, 5-7 cannot be followed. 



3. Determination of the Aspects. The cephalic (facial, "anterior," 

 or ectal), whether or not partly covered by the lids, is smooth and more 

 regularly convex and presents (in the sheep) an elliptical area surrounded 

 by a brown line. 



The caudal (cranial, "posterior," or ental) aspect may be hidden by 

 masses of fat and by the muscles ; if these have been partly removed the 

 remnants will still serve to distinguish this from the other. 



4. The Eyelids. Note that their ectal surface is hairy, and that 

 along the free margins are longer hairs, and less regular and less grace- 

 fully curved than the lashes of man ; they are more numerous on the up- 

 per lid, and from this may be determined the dorsal and ventral aspects 

 of the entire organ. The angles of junction of the lids are the mesal and 

 lateral CANTHI (commonly called "inner and outer"). 



a. The technical name for eyelashes is cilia (singular cilium); the 

 same word is applied to the microscopical, structureless, moving filaments 

 upon the mucosa of the air passages and some other parts. 



5. Between the eyeball and either lid insert a scalpel-handle, and 

 note that its passage is checked at about i cm. from the margin. Insert 

 a scissors-blade in the same way about one-third of the distance from 

 either can thus and transect the lid ; repeat at one-third of the distance 

 from the other canthus. 



6. The Meibomian Glands. Reflect the middle third of the lid, 

 demarcated as above and note that the ental surface, near the margin 

 presents a series of dark stripes, 3-4 mm. long, corresponding with small 

 orifices at the margin. These are the MEIBOMIAN GLANDS. 



a. The Meibomian glands secrete an oily matter which anoints the margin of the 

 lid and prevents the usually small amount of liquid between the eyeball and the lid from 

 running over the edge upon the face. The action may be illustrated as follows : 



Nearly fill two glasses with water. Wet the edge of one. Dry the 

 edge of the other and anoint it with sweet oil or other oily or fatty sub- 

 stance. Then carefully pour in water till both glasses are full to the brim. 

 The wetted brim permits the overflow at once but in the other glass the 

 water may rise perceptibly above the rim before it passes over the oil. 



7. The Conjunctiva. The smooth membrane lining the ental sur- 

 face of the lids is the CONJUNCTIVA. Note that it is continuous with the 

 ectal hairy skin at the smooth margin of the lid, just as the mucosa of 

 the mouth is continuous with the skin at the lips. 



a. Note also that it is reflected from the lid upon the surface of the 

 ball. When the lids have not been retained with the eye the cut edge of 

 the conjunctiva may be traced, and in places lifted slightly with the 

 tracer or forceps. 



