ORGANS OF THE SENSES. 523 



auricle to the bone, while its movements are effected, in part, 

 by muscular fibres which pass between the prominent parts of 

 its constituent cartilages, but mainly, by three small muscles 

 of the striped variety, and each of which has received a dis- 

 tinct name. 



The Auditory Canal. The auditory canal consists of two 

 parts, a cartilaginous and an osseous ; the first is formed 

 by the prolongation inwards of the cartilages of the auricle ; 

 these form a tube, deficient at the upper and back part, 

 where the place of cartilage is supplied by a fibrous mem- 

 brane ; this tube is inserted into the auditory process of 

 the temporal bone : the osseous part of this canal is formed 

 by the auditory process already alluded to ; this process in 

 the adult is nearly three-quarters of an inch long, and to its 

 outer margin the tympanum is attached, the bone being 

 grooved for its reception : in the foetus, the auditory process 

 is a detached ring of bone, into which, however, the tym- 

 panum is inserted. 



The orifice of the rneatus is defended by hairs, the bases 

 of which are in connection with sebaceous glands ; still 

 further inwards, but limited to the cartilaginous part of the 

 passage, the ceruminous glands are encountered : these have 

 already been described. 



According to some observers, muscular fibres exist in the 

 external meatus, which becomes shortened by their con- 

 traction. 



The Middle Ear. 



The middle ear consists of the tympanum, tympanic cavity, 

 and the ossicles with their muscles. 



The tympanum, or tympanic membrane, is divisible into 

 three laminas an external or cuticular, a middle or fibrous, 

 and an internal or ciliated ; the external is a continuation of 

 the cuticle which lines the external meatus, and may be 

 separated as a distinct membrane; the fibrous tissue, of 

 which the internal lamina of the tympanum is composed, is 

 strong and dense, and is arranged in a radiated manner ; into 



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