154: SPECIAL SENSES. 



tion 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 supe- 

 rior 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, becom- 

 ing thinner from without inward. In the osseous portion, 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. 1 



General Arrangement of the Parts composing the Middle 

 Ear. Without a very elaborate and minute anatomical de- 

 scription, 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 mi- 

 nute 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 cer- 

 tain of the most important structures. In beginning the dif- 

 ficult task of describing the physiological anatomy of the 

 middle and internal ear, it will be convenient to give a gen- 

 eral outline of the different parts, with their names. This, 

 with a careful study of Figs. 10, 11, 12, and 13, can hardly 

 fail to greatly facilitate the closer investigation of the more 

 important structures. 



The arrangement of the parts constituting the external 



1 See vol. iii., Secretion, pp. 60, 69. 



