1300 



SURFACE ANATOMY AND SURFACE MARKINGS 



Optic disc 



Macula lutea 



Solera 

 Choroid 



Retina 

 FIG. 1206. The interior, of the posterior half of the left eyeball. 



The Ear. The various prominences and fossae of the auricula (see page 1034) 

 are visible (Fig. 1 207) . The opening of the external acoustic meatus is exposed by 



drawing the tragus forward; at the orifice are a few 

 short crisp hairs which serve to prevent the entrance 

 of dust or of small insects; beyond this the secretion 

 of the ceruminous glands serves to catch any small 

 particles which may find their way into the meatus. 

 The interior of the meatus can be examined through 

 a speculum. At the line of junction of its bony 

 and cartilaginous portions an obtuse angle is formed 

 which projects into the antero-inferior wall and 

 produces a narrowing of the lumen in this situation. 

 The cartilaginous part, however, is connected to the 

 bony part by fibrous tissue which renders the outer 

 part of the meatus very movable, and therefore by 

 drawing the auricula upward, backward, and slightly 

 outward, the canal is rendered almost straight. In 

 children the meatus is very short, and this should 

 be remembered in introducing the speculum. 



Through the speculum the greater part of the tym- 

 panic membrane (Fig. 1208) is visible. It is a pearly- 

 gray membrane slightly glistening in the adult, placed 

 obliquely so as to form with the floor of the meatus an angle of about 55. At 

 birth it is more horizontal and situated in almost the same plane as the base of the 

 skull. The membrane is concave outward, and the point of deepest concavity 

 the umbo is slightly below the center. Running upward and slightly forward 

 from the umbo is a reddish-yellow streak produced by the manubrium of the 

 malleus. This streak ends above just below the roof of the meatus at a small 

 white rounded prominence which is caused by the lateral process of the malleus 

 projecting against the membrane. The anterior and posterior malleolar folds 

 extend from the prominence to the circumference of the membrane and enclose 

 the pars flaccida. Behind the streak caused by the manubrium of the malleus a 

 second streak, shorter and very faint, can be distinguished; this is the long crus 



FIG. 1207. The auricula or pinna. 

 Lateral surface. 



