THE ORGANS OF SPECIAL SENSE 



the first molar tooth, and should push his probe onward in such a way as if he desired to reach 

 this structure. 



Beneath the internal angular process of the frontal bone the pulley of the Superior oblique 

 muscle of the eye can be plainly felt by pushing the finger backward between the upper and inner 

 angle of the eye and the roof of the orbit; passing backward and outward from this pulley, the 

 tendon can be felt for a short distance. 



Applied Anatomy. The eyelids are composed of various tissues, and consequently are liable 

 to a variety of diseases. The skin which covers them is exceedingly thin and delicate, and is 

 supported on a quantity of loose and lax subcutaneous tissue which contains no fat. In conse- 

 quence of this it is very freely movable, and is liable to be drawn down by the contraction of 

 neighboring cicatrices. Such contractions may produce an eversion of the lid known as ectropion. 

 Inversion of the lids (entropion) from spasm of the Orbicularis palpebrarum or from chronic 

 inflammation of the palpebral conjunctiva may also occur. In some individuals there is an 

 extra row of eyelashes on the inner margin of the lid, directed toward the cornea (distichiasis). 

 Trichiasis is a condition in which the lashes are directed toward the eye, but the^e is not inversion 

 of the lid. The eyelids are richly supplied with blood, and are often the seat of vascular growths, 

 such as ncevi. Rodent ulcer also frequently commences in this situation. The loose cellular tissue 

 beneath the skin is liable to become extensively infiltrated either with blood or inflammatory 

 products, producing very great swelling. Even from very slight injuries to this tissue the extrava- 

 sation of blood may be so great as to produce considerable swelling of the lids and complete 

 closure of the eye, and the same is the case when the inflammatory products are poured out. The 

 follicles are liable to become inflamed, constituting the disease known as marginal blepharitis, 

 blepharitis ciliaris, or "blear-eye." Irregular or disorderly growth of the eyelashes not infre- 

 quently occurs, some of them being turned toward the eyeball and producing inflammation and 

 follicles of the eyelashes, or the sebaceous glands associated with these follicles may be the seat of 

 inflammation, constituting the ordinary hordeolum or "sty." The Meibomian glands are affected 

 in the so-called "tarsal tumor;" the tumor, according to some, being caused by the retained secre- 

 tion of these glands; by others it is believed to be a neoplasm connected with the gland. The 

 Orbicularis palpebrarum may be the seat of spasm (blepharospasm), either in the form of slight 

 quivering of the lids or repeated twitchings, most commonly due to errors of refraction in children, 

 or more continuous spasm, due to some irritation of the trigeminal or facial nerves. The Orbicu- 

 laris may be paralyzed, generally associated with paralysis of the other facial muscles. Under 

 these circumstances the patient is unable to close the lids, and if he attempts to do so, rolls the 

 eyeball upward under the upper lid. The tears overflow from displacement of the lower lid, 

 and the conjunctiva and cornea, being constantly exposed and the patient being unable to wink, 

 become irritated from dust and foreign bodies. As a result there may be ulceration of the 

 cornea, and possibly eventually complete destruction of the eye. In paralysis of the Levator 

 palpebrae superioris there is drooping of the upper eyelid (ptosis) and other symptoms of impli- 

 cation of the oculomotor nerve. The eyelids may be the seat of bruises, wounds, or burns. After 

 wounds or burns adhesions of the margins of the lids to each other or adhesion of the lids to 

 the globe may take place. The eyelids are sometimes the seat of emphysema after fracture of 

 some of the thin bones forming the inner wall of the orbit. If shortly after such an injury the 

 patient blows his nose, air is forced from the nostrils through the lacerated structure into the 

 connective tissue of the eyelids, which suddenly swell up and present the peculiar crackling on 

 pressure which is characteristic of this affection. 



Foreign bodies frequently get into the conjunctival sac and cause great pain, especially if 

 they come in contac* with^the corneal surface, during the movements of the lid and the eye on 

 each other. The conjunctiva is frequently involved in severe injuries of the eyeball, b ut is seldom 

 ruptured alone; the most common form of injury to the conjunctiva alone is from a burn, either 

 from fire, strong acids, or lime. In these cases the union is apt to take place between the eyelid 

 and the eyeball. The conjunctiva is often the seat of inflammation arising from many different 

 causes, and the arrangement of the conjunctival vessels should be remembered as affording a 

 means of diagnosis between this condition and injection of the sclera, which is present in inflam- 

 mation of the deeper structures of the globe. The inflamed conjunctiva is bright red; the 

 vessels are large and tortuous, and greatest at the circumference, shading off toward the corneal 

 margin; they anastomose freely and form a dense network, and they can be emptied by gentle 

 pressure. 



The lacrimal gland is occasionally, though rarely, the seat of inflammation (dacri/o(tdctuti\ 

 either acute or chronic; it is also sometimes the seat 'of tumors, benign or malignant, and for these 

 may require removal. This may be done by an incision through the skin just below the eyebrow ; 

 and the gland, being invested with a special capsule of its own, may be isolated and removed 

 without opening the general cavity of the orbit. The canals may be' obstructed, either as a con- 

 genital defect or by some foreign body, as an eyelash or a dacryolith, causing the tears to run 

 over the cheek. The canals may also become occluded as the result of burn* or injury; over- 

 flow of tears may, in addition, result from deviation of the puncta or from chronic inflammation 

 of the lacrimal sac. When there is failure of the lacrimal tubes to drain off the tears and the 



