THE EXTERNAL EAR 



871 



(which are chiefly elastic), the integument, and a complicated arrangement of 

 muscles. 



The conchal or auricular cartilage (Cartilago auriculae) determines the shape 

 of the ear; its form can be made out in a general way without dissection, except 

 below, where it is concealed by the muscles and the parotid gland. The basal part 

 is coiled so as to form a tube, which encloses the cavity of the concha (Cavum con- 

 chae). This part is funnel-shaped and curves outward and a little backward. Its 

 medial surface is strongly convex, forming a prominence termed the eminentia 

 conchae. The lowest part of the medial margin bears a narrow, pointed prolongation, 

 the styloid process. This process is about an inch long and projects downward 

 over the annular cartilage; the guttural pouch is attached to its free end. Behind 

 its base there is a foramen through which the auricular branch of the vagus passes. 



The basal part of the posterior border is cut into by a notch, which separates two irregular 

 quadrilateral plates. The upper plate (Tragus) is overlapped by the anterior border, and is sep- 

 arated from the adjacent part of the posterior border (Antitragus) by a notch (Incisura inter- 

 tragica) . The lower plate is curved to form a half ring and partly overlaps the anterior border and 

 the annular cartilage. Behind the notch there is a foramen, which transmits the internal auricular 

 artery and internal auricular branch of the facial nerve. 



The annular cartilage (Cartilago annularis) is a quadrilateral plate, curved to 

 form about three-fourths of a ring; its 

 ends are a little less than half an inch (ca. 

 1 cm.) apart medially and are united by 

 elastic tissue. It embraces the external 

 acoustic process and forms with the lower 

 part of the conchal cartilage the carti- 

 laginous part of the external acoustic 

 meatus. 



The scutiform cartilage (Cartilago 

 scutiformis s. Scutulum) is an irregular 

 quadrilateral plate which lies on the tem- 

 poral muscle in front of the base of the 

 conchal cartilage. Its superficial face is 

 slightly convex from side to side and 

 its deep face is correspondingly concave. 

 The anterior end is thin and rounded; the 

 posterior part or base is wider and thicker, 

 and its medial angle is prolonged by a 

 pointed process half an inch or more in 

 length. The cartilage moves very freely 

 over the underlying parts. 



The external acoustic meatus leads 

 from the cavum conchse to the tympanic 

 membrane. It does not continue the 

 general direction of the cavity of the 

 concha, but extends medially, downward, 

 and slightly forward. It consists of a cartilaginous part (Meatus acusticus ex- 

 ternus cartilagineus) which is formed by the lower part of the conchal cartilage 

 and the annular cartilage, and an osseous part formed by the external acoustic 

 process of the temporal bone. These are united by elastic membranes to form a 

 complete tube. Its caliber diminishes medially, so that the lumen of the inner end 

 is about half of that of the outer end. . , . . 



The skin on the convex surface of the concha presents no special features; it 

 is attached to the cartilage by a considerable amount of subcutaneous tissue except 

 at the apex The integument which lines the concave surface is intimately ad- 



Fig. 699. — Conchal and Annular Cartilages of 

 Ear of Horse, External View. 

 1, Base of concha; 2, posterior border, 3, anterior 

 border of concha; -f, intertragic notch; 5, eminentia 

 concha; 6, styloid process; 7, annular cartilage; 9, 

 zygomatic arch. (After EUenberger-Baum, Anat. fiir 

 Kunstler.) 



