1114 THE ORGANS OF SPECIAL SENSE 



and tiresome efforts at accommodation. The condition is usually due to inordinate shortness of 

 the axis of the eye, but may be due to loss of the lens, decreased convexity of the refractive sur- 

 faces, or lessened refractive power in the refractive media of the eye. It is corrected by the use 

 of convex glasses. 



Myopia is near-sightedness. In this condition the rays of light come to a focus in front of the 

 retina, and the patient is subjected to continued eye-strain. It is usually due to too great length 

 of the axis of the eye, but may result from increase in refractive power of refractive media. It is 

 corrected by concave glasses. Sometimes, as a person with hyperopia begins to age, an increased 

 refractive power of the lens causes myopia. The occurrence of myopia in a hyperopic eye is 

 called second sight, and it enables the individual to cease wearing convex glasses. 



Exenteration of the contents of the orbit means removal of all the contents except those at the 

 orbital apex. Even the periosteum is taken away. It is performed for malignant disease. 



Evisceration of the eyeball is performed by making a circular incision at the corneal margin and 

 removing the internal and middle coats and the contents of the globe. The sclera is not removed. 

 A glass ball is inserted into the scleral sheath, and the sclera is closed over the ball by vertical 

 stitches, and the conjunctiva is closed over it by transverse stitches. The operation is performed 

 for leucoma or staphylorna of the cornea. An artificial eye (a shell) is placed over the stump 

 when healing is complete. 



Enucleation, or excision of the eyeball, differs from exenteration of the orbital contents in the 

 fact that only the eyeball is removed. A circular incision through the ocular conjunctiva is 

 carried around and near to the corneal margin. The conjunctiva and capsule of Tenon are 

 pushed back and the Rectus muscles are clamped and divided back of the clamp. Traction 

 is made upon the globe in a forward and inward direction, and the optic nerve and adjacent 

 structures are cut with scissors from the outer aspect of the globe. The eye is then pulled out of 

 the orbit, and all structures which tend to retain it are divided. The stumps of the Recti muscles 

 are sewed together. 



THE APPENDAGES OF THE EYE (ORGANA OCULI ACCESSORIA). 



The appendages of the eye include the eyebrows, the eyelids, the conjunctiva, 

 and the lacrimal apparatus viz., the lacrimal gland, the lacrimal sac, and the nasal 

 duct. 



The Eyebrows (supercilia) are two arched eminences of integument which sur- 

 mount the upper circumference of the orbit on each side, and support numerous 

 short, thick hairs, directed -obliquely on the surface. The hairs may entangle 

 foreign bodies and lessen somewhat the force of blows. In structure the eyebrows 

 consist of thickened integument, connected beneath with the Orbicularis palpe- 

 brarum, Corrugator supercilii, and Occipitofrontalis muscles. These muscles 

 serve, by their action on this part, to control to a certain extent the amount of 

 light admitted into the eye. 



The Eyelids (palpebrae) (Figs. 823 and 824) are two thin, movable folds placed 

 in front of the eye, and protecting it from injury by their closure. The eyelids 

 are composed of skin, superficial fascia, and areolar tissue, fibres of the Orbicu- 

 laris palpebrarum muscle, palpebral and orbitotarsal ligaments, tarsal plates, 

 and conjunctiva. The upper lid also contains the Levator palpebrae superioris 

 muscle. In the lids are bloodvessels, lymph vessels, nerves, and Meibomian 

 glands. There are two lids, the upper (palpebra superior) and the lower (palpcbra 

 inferior)} the groundwork of both lids is made up of a fascial membrane called 

 the orbital septum (septum orbitale). The upper lid is the larger and the more 

 movable of the two, and is furnished with a separate elevator muscle, the Levator 

 palpebrae superioris. The orbital septum, in each lid, consists of two portions. 

 The part near the orbital margin is called the orbital portion (pars orbitalis). 

 The part in which the tarsus lies is called the tarsal portion (pars tarsalis). Between 

 the two portions in each lid is a sulcus, called, in the upper lid, the superior orbito- 

 palpebral sulcus (sulcus orbitopalpebralis superior), and, in the lower lid, the inferior 

 orbitopalpebral sulcus (sulcus orbitopalpebralis inferior). When the eyelids are 

 opened an elliptical space, the interpalpebral slit (rima palpebrarum), is left between 



