446 Anatomy Applied to Medicine and Surgery. 



portion points forwards and inwards, and consequently, to 

 make the canal sufficiently straight so as to clearly see the 

 membrana tympani, the outer or moveable part must be 

 brought into a straight line with the inner fixed portion 

 and this is done by drawing the pinna upwards and back- 

 wards. The angle formed by the junction of these two 

 portions of the external auditory meatus is the narrowest 

 as well as the highest point of the canal. The lining 

 membrane of the meatus is continuous with the skin and 

 is supplied, in, its cartilaginous part, with hairs, cerumi- 

 nous glands and sebaceous glands. The outer end of the 

 canal is oval in shape from above downwards, while the 

 inner end is oval from before backwards, and, since the 

 inner end of the meatus is closed by the membrana tym- 

 pani and since the latter is directed obliquely downwards, 

 inwards and forwards, it follows that the anterior and the 

 inferior walls of the canal must be longer than the pos- 

 terior and the superior walls. The nervous supply of the 

 external auditory canal is from the auriculo-temporal and 

 from the pneumogastric through Arnold's branch. 



Nerve Reflexes. Irritation of the branches of either 

 of the divisions of the fifth nerve may induce earache, since 

 the auriculo-temporal, which supplies the auditory canal, 

 is also a branch of the fifth nerve through its inferior 

 maxillary division. This may be seen, clinically, where 

 inflammation of the eye is accompanied by pain in the ear, 

 (ophthalmic), or where caries of the upper teeth (dental 

 branches of the superior maxillary) or of the lower teeth 

 (inferior dental from the inferior maxillary) are associa- 

 ted with earache. When pain in the tongue is referred to the 

 ear it is probably through the lingual branch of the inferior 

 maxillary. Arnold's nerve brings the pneumogastric into 

 connection with the external meatus, so that the introduc- 

 tion of instruments into, or the presence of foreign bodies 

 in the meatus may cause nausea, vomiting, etc. 



