848 THE ORGANS OF SPECIAL SENSE. 



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

 of the palpebral conjunctiva may also occur. The eyelids are richly supplied with blood, and are 

 often the seat of vascular growths, such as naevi. Rodent ulcer also frequently commences in 

 this situation. The loose cellular tissue beneath the skin is liable to become extensively infil- 

 trated either with blood or inflammatory products, producing very great swelling. Even from 

 very slight injuries to this tissue the extravasation of blood may be so great as to produce consid- 

 erable swelling of the lids and complete closure of the eye, and the same is the case when inflam- 

 matory products are poured out. The follicles of the eyelashes or the sebaceous glands associated 

 with these follicles maybe the seat of inflammation, constituting the ordinary " sty. " The 

 Meibomian glands are affected in the so-called " tarsal tumor ; " the tumor, according to some, 

 being caused by the retained secretion of these glands ; by others it is believed to be a neoplasm 

 connected with the gland. The ciliary follicles are liable to become inflamed, constituting the 

 disease known as blepharitis ciliaris, or " blear-eye." Irregular or disorderly growth of the eye- 

 lashes not unfrequently occurs, some of them being turned toward the eyeball and producing 

 inflammation and ulceration of the cornea, and possibly eventually complete destruction of the 

 eye. The Orbicularis palpebrarum may be the seat of spasm, either in the form of slight quiv- 

 ering 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 fifth or seventh cranial nerve. The 

 Orbicularis 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. In paralysis of the Levator palpebrae 

 superioris there is drooping of the upper eyelid and other symptoms of implication of the third 

 nerve. The eyelids may be the seat of bruises, wounds, or burns. In these latter injuries adhe- 

 sions 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 nostril through the lacerated structures into the connective tissue of 

 the eyelids, which suddenly swell up and present the peculiar crackling characteristic of this 

 affection. 



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

 they come in contact 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, but 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 union is liable 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 sclerotic, which is 

 present in inflammation 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 or displaced by gentle pressure. 



The lachrymal gland is occasionally, though rarely, the seat of inflammation, 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 canaliculi may be obstructed, either as a 

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

 over the cheek. The canaliculi may also become occluded as the result of burns or injury ; over- 

 flow of the tears may in addition result from deviation of the puncta or from chronic inflamma- 

 tion of the lachrymal sac. This latter condition is set up by some obstruction to the nasal duct 

 frequently occurring in tubercular subjects. In consequence of this the tears and mucus accumu- 

 late in the lachrymal sac, distending it. Suppuration in the lachrymal sac is sometimes met 

 with ; this may be the sequel of a chronic inflammation ; or may occur after some of the erup- 

 tive fevers in cases where the lachrymal passages were previously quite healthy. It may lead to 

 lachrymal fistula. 



THE EAE. 



The organ of hearing is divisible into three parts the external ear, the middle 

 ear or tympanum, and the internal ear or labyrinth. 



The External Ear. 



The external ear consists of an expanded portion named pinna or auricle, and 

 the auditory canal or meatus. The former serves to collect the vibrations of the air 

 by which sound is produced ; the latter conducts those vibrations to the tympanum. 



The pinna, or auricle (Fig. 455), is of an ovoid form, with its larger end directed 



