1056 



SPECIAL SENSE ORGANS 



(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 downward. These figures refer to the adult male; in the female the eyeball 

 is .5 mm. smaller in all axes. Again, if the globe is divided in its mid-sagittal 

 plane, the nasal division will be found to be sUghtly 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 conjoint^ by the cornea and sclera, the entire outer surfaces of which are 

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

 the cornea there remains a little adherent conjunctiva; elsewhere, the sclera is 

 directh' 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 inser- 

 tions of the two oblique muscles — that of the superior oblique tendinous, and 

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

 nerve and the lateral rectus. 



Fig. 800. — Diagrammatic View of the Insertions of the Ocular Muscles. 



Superior rectus 



Lareral rectus 



Lateral rectus 



Inferior 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 toward us, and in the natural position with the superior oblique tendon 

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

 and we can consequently determine the different recti muscles. 



The medial [rn. rectus medialis] rectus is inserted nearest (5.5 to 7 mm. from) the corneal 

 border; the superior [m. rectus superior] rectus commonly, sometimes the lateral [m. rectus 

 lateralis], is inserted furthest from it (7.7 to 8 mm.). All the recti tendons are broad and thin, 

 but that of the medial is the broadest (8 to 10.3 mm.); those of the lateral and inferior the 

 narrowest (6 to 9.2, or 9.8 mm., respectively). The greatest interval between two neighbouring 

 tendons is that between the superior and medial recti (about 12 mm.); tlie least is between 

 the superior and lateral (7 mm.). The form of the lines of insertion of the different tendons 

 varies considerably, the inferior being almost straight, the superior and lateral convex forward, 

 the medial further removed from the corneal border below than above. 



The in.scrtions of the oblique muscles [mm. obliqui] are at more than double the average 

 distance of the insertions of the recti from the corneal border. That of the superior obhque is 

 found on the superior surface of the sclera, about sixteen millimetres from the corneal edge, 

 in the form of a line 10.7 mm. long sloping from before backward and medially. The inferior 

 oblique has a long fleshy insertion lying between the lateral rectus and the optic nerve entrance; 

 the posterior end of the insertion, which is also the higher, is only about five to six millimetres 

 from tlie optic nerve, and from this i)oint it slopes forward, laterally, and slightly downward. 



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

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

 two arteries are the long posterior ciliary [aa. ciiiarosposteriores longi]; they both 

 jxjrforate the globe in the horizontal nuM-idian, 3. 5 mm. from the optic nerve, one 

 on the lateral, the other on the medial, side. The short ciliary arteries [aa. ciliares 



