II 



THE ORGANS OF SPECIAL SENSE 



THE organs of special sense include the nose 3 the ear and the 

 eye. 



THE EAR, OR ORGAN OF HEARING, 



consists of three parts, namely (i) The AURICLE and the 

 EXTERNAL ACOUSTIC MEATUS, (2) the CAVUM TYMPANI or 

 MIDDLE EAR, and (3) the INTERNAL EAR. 



The skin of the Auricle receives its nerve-supply from two 

 quite different sources. Its postero-inferior part is supplied 

 from the cervical plexus through the great auricular nerve 

 (C. 2, 3), but its antero-superior part is supplied from the fifth 

 cerebral nerve through the auriculo-temporal branch of the 

 mandibular division (Fig. 40). 



The External Acoustic Meatus is about i inch in length, 

 and is partly cartilaginous and partly osseous. At its medial 

 extremity the meatus is closed by the tympanic membrane, 

 which is set obliquely so that its lateral surface is directed 

 forwards and downwards as well as laterally. Examination 

 of the membrane by reflected light is rendered more difficult 

 on account of the bends which occur in the meatus. The 

 cartilaginous portion, which forms the lateral third, passes 

 medially, forwards and upwards ; the lateral part of the 

 osseous portion passes medially and backwards, while the rest 

 of the canal is directed medially, forwards and slightly down- 

 wards. In order to obtain the best possible view of the 

 membrane, it is necessary to bring the movable cartilaginous 



