25i 



ANIMAL PHYSIOLOGY. 



complicated to produce an organ capable of appreciating the 

 fine varieties of sound, but there are many accessory parts 

 added, which bring sounds within reach of the sensitive struc- 

 tures, and likewise protect these from over-stimulation. 



The human ear consists of three parts : the external, middle, 

 and internal ear. The internal ear is the essential organ of 

 hearing, filled with fluid, and containing the distribution of 

 the auditory nerve. The external and middle ears contain 

 air, the external ear being open to the outside, and the 

 middle ear or tympanum, as it is called, communicating with 

 the pharynx; and they are separated, one from the other, by 

 a partition, the membrana tympdni. 



Fig. 126. CARTILAGE AND MUSCLES OF EXTERNAL EAR. A, Outer 

 aspect. B, Cranial aspect, a, 6, c, attrahens, attollens, and retra- 

 liens auriculam muscles ; d, concha ; e, antihelix ; /, g, large and 

 small muscle of helix ; h, tragus and tragic muscle ; i, antitragus 

 and antitragic muscle; Jc, the edge of the cartilage which is 

 attached by fibrous tissue to the external auditory meatus of the 

 temporal bone ; I, tragus from behind ; m, transverse muscle cross- 

 ing the sulcus at the back of the antihelix; n, oblique muscle 

 crossing sulcus at the back of the inferior branch of the anti- 

 helix. The lobule is represented in dotted oiitline. 



