818 SPECIAL SENSES. 



The form of the pinna and its consistence depend upon the presence of fibro-cartilage, 

 which occupies the whole of the external ear except the lobule. This structure has 

 already been described in another chapter. 



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 sudoriparous and sebaceous glands. 



The muscles of the ear are not important in the human subject ; 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 attached to the sides of the head by two 

 distinct ligaments and a few delicate ligamentous fibres. 



The external auditory meatus is about an inch and a quarter 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 downward 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 portion being inclined outward, so that the inferior wall of the meatus is consid- 

 erably 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 continuation of the cartilage of the pinna, with fibrous tissue. 

 About the lower two-thirds of this portion of the canal is cartilaginous, the upper third 

 being fibrous. The rest of the tube is osseous and is a little longer and narrower than 

 the cartilaginous portion. Around the inner extremity of the canal, with the exception 

 of its superior portion, is a narrow groove, which receives the greater portion of the 

 margin of the membrana tympani. 



The skin of the external meatus is continuous with the integument covering the 

 pinna. It is very delicate, becoming thinner from without inward. In the osseous por- 

 tion, it adheres very closely to the periosteum, and, at the bottom of the canal, it is 

 reflected over the membrana tympani, forming its outer layer. In the cartilaginous and 

 fibrous portion, are numerous short, stiff hairs, with sebaceous glands attached to their 

 follicles, and the coiled tubes known as the ceruminous glands. The structure of these 

 glands and the properties and composition of the cerumen have already been described 

 under the head of secretion. 



General Arrangement of the Parts composing the Middle Ear. Without a very elabo- 

 rate and minute anatomical description, fully illustrated by plates, it is difficult to give a 

 clear idea of the structure and relations of the very complex apparatus of the middle and 

 the internal ear. Such a minute and purely anatomical description would be out of 

 place in this work, where it is desired only to give such an account of the anatomy as 

 will enable the student to comprehend the physiology of the ear, reserving for special 

 description certain of the most important structures. In beginning the difficult task of 

 describing the physiological anatomy of the middle and internal ear, it will be convenient 

 to give a general outline of the different parts, with their names. This, with a careful 

 study of Figs. 258, 259, 260, and 261, can hardly fail to greatly facilitate the closer in- 

 vestigation of the more important structures. 



The arrangement of the parts constituting the external ear is sufficiently simple. The 



middle ear presents a narrow cavity (Fig. 258, 11), of irregular shape, situated between 



ie external ear and the labyrinth, in the substance of the temporal bone. The general 



arrangement of its parts is shown in Fig. 258. The outer wall of the tympanic cavity is 



formed by the membrana tympani (Fig. 258, 6). This membrane is concave, its concav- 



