570 BULBUS OCULI 



BULBUS OCULI. 



THE bulbus oculi or eyeball is not perfectly spherical ; it may 

 be said to be composed of the segments of two spheres. 

 The anterior or corneal segment, forming only about one-sixth 

 of the entire eyeball, possesses a shorter radius than the pos- 

 terior or scleral segment. The anterior clear corneal part of 

 the eyeball forms, therefore, a dome-like bulging or prominence 

 on the front of the globe of the eye. The terms anterior 

 and posterior pole are respectively applied to the central points 

 of the anterior and posterior segments of the eyeball. The 

 imaginary line which joins these poles receives the name 

 of the sagittal axis, whilst another line drawn in a coronal 

 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 these 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, but it 

 is perhaps better that the student should begin with the eyeball of the 

 ox, seeing that in it the dissection can be more easily carried out. 



When the dissector has provided himself with six eyeballs obtained from 

 oxen, he should remove from them the conjunctiva, 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 these 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 posteriorly towards the 

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

 eyeball the venae vorticosae will be noticed issuing from the sclera at wide 

 intervals from each other, and on approaching the posterior aspect of the 

 eyeball the posterior ciliary arteries and the ciliary nerves will be seen 

 piercing the sclera around the entrance of the optic nerve. 



Before beginning the actual dissection of the eyeball, it is important 

 that the student should obtain a general conception of the parts which 

 compose it. This can be done by sections through three hardened speci- 

 mens in three different planes. One specimen may be divided at the 

 equator into an anterior and a posterior portion. Another may be divided 



