EXAMINATION OF Till': i-:vi-:n.\i.L 1023 



mal caruncle is in reality an island (if modified skin, and fine hairs can commonly 

 lie detected on its .surface. On its outer side, separated from it by a narrow groove, 

 is the semilunar fold of conjunctiva; it rests on the eyeball, and is a rudiment 

 of the third eyelid or nictitating membrane, present in birds and well represented 

 in many other vertebrates. 



EXAMINATION OF THE EYEBALL 



I he eyeball of a cadaver should now be removed by snipping with stissors the conjunctiva 

 near the conical border, then cutting through the ocular muscles near their insertion into the 

 globe, and finally dividing the optic nerve close to the sclerotic. 



The eyeball is almost spherical, but not perfectly so, mainly because its an- 

 terior, clear, or corneal segment has a greater curvature than the rest of the eye. 

 Considering it as a globe, however, we speak of an anterior and of a posterior 

 pole ; the former corresponding to the middle of the front of the cornea, the lat- 

 ter to the middle of the posterior curvature. An imaginary straight line joining 

 the two poles is called the antero- posterior or sagittal axis of the eyeball. The 

 equator of the eye is that part of its surface which lies midway between the two 

 poles. The sagittal axis of the globe is the greatest (about 24'5 mm.), the ver- 

 tical equatorial the least (about 23'5 mm.), and the transverse equatorial axis is 

 intermediate in length (about 23'9), so that the eyeball is in reality an ellipsoid, 

 flattened slightly from above downwards. Again, if the globe is divided in its 

 antero-posterior vertical plane, the nasal division will be found to be slightly smaller 

 than the temporal. The optic nerve joins the globe three or four millimetres to 

 the nasal side of the posterior pole. 



The shape of the eye depends on, and is preserved by, the outermost tunic, 

 formed conjointly by the cornea and sclerotic, the entire outer surfaces of which 

 are now in view. The anterior or corneal part has been already examined. All 

 around the cornea there remains a little adherent conjunctiva; elsewhere, the 

 sclerotic is directly exposed, except for some loose connective tissue which adheres 

 to it, especially around the optic nerve entrance. In front of the equator we see 

 the tendinous insertions of the four recti muscles. Behind the equator are the 

 insertions of the two oblique muscles that of the superior oblique tendinous, 

 and further forwards; that of the inferior more fleshy, and placed between the optic 

 nerve and the external rectus. 



It is difficult to recognise the different recti muscles by their insertions if we do not know 

 whether the eye examined is a right or a left one. To determine this we should hold the globe 

 with the optic nerve towards us, and in the natural position with the superior oblique tendon 

 uppermost. The inferior oblique tendon will now point to the side to whicli the eye belongs, and 

 we can consequently determine the different recti muscles. 



The internal rectus is inserted nearest (7 mm. from) the corneal border; the 

 external rectus commonly, sometimes the superior, is inserted furthest from it 

 (about 8 mm.). All the recti tendons are broad and thin, but that of the internal 

 is the broadest (8 mm.); those of the external and inferior the narrowest (6 mm.). 

 The greatest interval between two neighbouring tendons is that between the supe- 

 rior and internal recti (about 12 mm.); the least is between the superior and ex- 

 ternal (7 mm.). The form of the lines of insertion of the different tendons varies 

 considerably, the inferior being almost straight, the superior and external convex 

 forwards, the internal further removed from the corneal border below than above. 



The insertions of the obliques are at more than double the average distance of 

 the insertions of the recti from the corneal border. That of the superior oblique is 

 found on the superior surface of the sclerotic, about sixteen millimetres from the 

 corneal edge, in the form of a line sloping from before backwards and inwards. 

 The inferior oblique has a long fleshy insertion lying between the external rectus 

 and the optic nerve entrance: tin' posterior end of the insertion, which is also the 

 higher, is only about six millimetres from the optic nerve, and from this point 

 it slopes forwards, outwards, and slightly downwards. 



.Several small nerves and two arteries may be seen running forwards and ulti- 

 mately perforating the sclerotic not far from the entrance of the optic nerve. The 

 two arteries are the long posterior ciliary : they both perforate the globe in the hori- 

 zontal meridian, one on the outer, the other on the inner, side. The short ciliary 



