532 BULBUS OCULI 



anterior, clear corneal part of the eyeball appears, therefore, 

 as a convex window or prominence on the front of the 

 globe of the eye. The terms anterior pole and posterior fole 

 are respectively applied to the central points of the anterior 

 and posterior segments of the eyeball. The imaginary line 

 which joins the two poles receives the name of the sagittal 

 axiS) whilst another line drawn in a frontal direction around 

 the globe of the eye, midway between the two poles, so as 

 to divide the eyeball into two hemispheres, is termed the 

 equator. Imaginary meridional lines also are drawn between 

 the two poles so as to cut the equatorial line at right angles. 



Dissection of the Eyeball. A satisfactory dissection of the 

 globe of the eye can be made only when the eyeball is fresh, or 

 after it has been hardened for several days in a 10% solution 

 of formol. In the dissecting-room it is often impossible to 

 obtain suitable specimens ; but it is always easy to procure 

 eyeballs of the pig, sheep, or ox, and those suit the purpose 

 admirably. It is advisable, however, that the dissector should 

 complete his study of the organ by the examination of a fresh 

 human eyeball obtained from the post-mortem room. In point 

 of size, and also in other particulars, the eyeball of the pig more 

 closely resembles the human eyeball than the eyeball of the 

 sheep or ox ; but it is perhaps better that the student should 

 begin with the eyeball of the ox, because the necessary dissection 

 can be more easily carried out in it than in smaller eyeballs. 



When the dissector has provided himself with six eyeballs 

 obtained from oxen, he should remove from them the conjunc- 

 tiva, fascia bulbi, ocular muscles, and fat, which adhere to 

 them. Pinching up, with the forceps, the conjunctiva and the 

 fascia bulbi close to the corneal margin, he should snip through 

 those layers with the scissors and divide them round the whole 

 edge of the cornea. He can then easily strip all the soft parts 

 from the surface of the sclera, working steadily backwards 

 towards the entrance of the optic nerve. A little posterior to 

 the equator of the eyeball the vence vorticosce will be noticed 

 issuing from the sclera, at wide intervals from each other ; and 

 as the posterior aspect of the eyeball is approached the posterior 

 ciliary arteries and the ciliary nerves will be seen piercing the 

 sclera around the entrance of the optic nerve. 



Before the student begins the actual dissection of the eyeball, 

 it is important that he should obtain a general conception of 

 the parts which compose it. That can be done by sections made 

 through three hardened specimens in three different planes. 

 One specimen should be divided, at the equator, into an anterior 

 and a posterior portion. Another should be divided, in an 

 antero-posterior direction, into a medial and a lateral half. A 

 third should be divided horizontally and a portion of the vitreous 

 body should be removed (Fig. 226). When the sections are 

 made, they should be placed under water in a cork-lined tray, 

 and preserved for reference as the study of the eyeball is pro- 

 ceeded with. 



