434 NERVOUS SYSTEM. 



on which circumstance it depends for the permanency of its 

 shape. 



The ear, of common language, is divided into two parts, Pin- 

 na* and Lobus : the former is the most extensive, as it compre- 

 hends all the cartilaginous portion: the latter is attached to the 

 inferior margin of the former, and, having no cartilage in its 

 composition, is soft and pendulous. 



In the centre of the external ear is a deep depression called 

 the Concha; in the bottom of it is the orifice of the canal lead- 

 ing to the tympanum, and called Meatus Auditorius Externus. 

 The circumference of the pinna is convoluted into a scroll called 

 the Helix, and commences just above the meatus by a ridge. 

 This ridge divides the concha into two unequal cavkies, of 

 which the lower is the larger. The scroll becomes gradually 

 less prominent, till it terminates at the posterior inferior part of 

 the pinna, in the lobus. 



The Antihelix is the slightly curved arid vertical eminence in 

 the middle of the pinna : its lower part forms the posterior boun- 

 dary of the concha, and its upper part bifurcates into two small 

 ridges, between which there is a depression called the Scapha. 

 Between the antihelix and the posterior half of the helix, is an 

 oblong depression called the Fossa Innominata. 



The Tragus is a cartilaginous elevation of the pinna placed 

 in front of the concha, and inclining somewhat over it; opposite 

 to it, at the inferior part of the concha, is the Antitragus. 



The cartilaginous plate, upon which the external ear depends 

 for its shape, is of a thickness very nearly uniform; of course, 

 the ridges and depressions on its exterior surface have corre- 

 sponding depressions and ridges on the side next to the head. It 

 is interrupted at several places by fissures ; for example, there 

 is one of considerable size filled up with ligamentous matter, 

 which separates the upper margin of the tragus from the be- 

 ginning of the helix: there is another between the lower extre- 

 mity of the antihelix and the antitragus. In the tragus, there 

 are two, and sometimes three, small narrow ones, said, by San- 

 torini, to be filled with muscular fibres; but the latter assertion 



* From some resemblance to a certain shell fish. 



