714 



SPECIAL SENSES 



rounding the opening of the meatus is called the concha. A small 

 lobe projects posteriorly, covering the anterior portion of the concha, 

 which is called the tragus; and the projection at the lower extremity of 

 the antihelix is called the antitragus. The fleshy dependent portion of 

 the pinna is called the lobule. 



The form of the pinna and its consistence depend on the presence 

 of elastic cartilage, which occupies the entire external ear except the 

 lobule. The structure of this kind of cartilage has already been de- 

 scribed (see Plate X, Fig. 4). 



The integument covering the ear does not vary much from the 

 integument of the general surface. It is thin, closely attached to the 

 subjacent parts, and possesses small rudimentary hairs, with sudoripa- 

 rous and sebaceous glands. 



The muscles of the external ear 

 are not important in the human sub- 

 ject ; and excluding a few exceptional 

 cases, they are not under the control 

 of the will. The extrinsic muscles are 

 the superior, or attollens, the anterior, 

 or attrahens, and the posterior, or 

 retrahens aurem. In addition there 

 are the six small intrinsic muscles, 

 situated between, the ridges upon the 

 cartilaginous surface. The pinna is 

 Fig. j.%4.- Posterior view of a mould attached to the sides of the head by 



in wax of the cavity of the concha and the . 



external auditory meatus (Sappey). two distinct ligaments and a few dell- 



cate ligamentous fibres. 



The external auditory meatus is about an inch and a quarter (31.8 

 millimeters) in length and extends from the concha to the membrana 

 tympani. Its course is somewhat tortuous. Passing from without 

 inward, its direction is at first somewhat upward, turning abruptly over 

 a bony prominence near the middle, from which it has a slightly down- 

 ward direction to the membrana tympani. Its general course is from 

 without inward and slightly forward. The inner termination of the 

 canal is the membrana tympani, which is quite oblique, the upper por- 

 tion being inclined outward, so that the inferior wall of the meatus is 

 considerably longer than the superior. 



The walls of the external meatus are partly cartilaginous and fibrous, 

 and partly bony. The cartilaginous and fibrous portion occupies a 

 little less than one-half of the entire length and consists of a continua- 

 tion of the cartilage of the pinna, with fibrous tissue. The lower two- 

 thirds of this portion of the canal is cartilaginous and the upper third 



