SENSITIVE SYSTEM. 395 



The annular cartilage, ring-like in its shape, surrounds 

 the auditory process of the temporal bone, in which situation it 

 is embraced by the lower end of the conchal cartilage, the two 

 being connected bv ligamentous substance. It forms the en- 

 trance or beginning of the meatus auditorius externus. — Its use 

 appears to be, to admit of the motions of the external ear, and, 

 at the same time, preserve the meatus from sustaining obstruc- 

 tion or interruption in its canal in consequence of such move- 

 ments, whereby sound might be checked or arrested in its way 

 to the interior. 



The scutiform, or triangular cartilage (wrongly 

 called triaiigidar, however, since its form bears a nearer approach 

 to an oval, flattened), is situated at the inner and fore part of the 

 base of the conchal cartilage, reposing upon the temporal muscle. 

 It gives attachment to several of the muscles moving the ear. 



THE SKIN covering the ear, although continuous with the 

 other common integument of the body, exhibits within the cavity 

 of the concha a comparatively thin and delicate texture. It 

 becomes very thin and dry; and adheres to the cartilage by a 

 cellular tissue, dense and compact, and destitute of adipose 

 substance. After having lined the conchal cavity, it ends in a 

 sort of blind pouch over the membrane of the tympanum, to 

 which it contributes an outward layer. Underneath the skin we 

 find numerous follicles, from which oozes a peculiar greasy mat- 

 ter, for the purpose of keeping the parts soft and pliant. Below 

 these follicles there is a second set of glands — the glandula. 

 ceruminos(£ ; whose ducts open between the roots of the hairs, 

 and issue a sticky bitter matter, which, acquiring consistence 

 from evaporation, constitutes the cerumen or wax of the ear. 

 This secretion protects the bottom of the ear from the insinuation 

 of insects, dust, &c. Sometimes it collects and forms concre- 

 tions, obstructing the passage into the interior. 



Organization, — The arteries supplying the external ear are 

 derived from the anterior and posterior auricular branches of the 

 external carotid. Its veins return their blood into the jugular. 

 Its nerves come from the portio dura of the seventh pair. 



Meatus Auditorius Externus. 

 The external auditory passage \H the tubular canal leading from 

 the cavity of the concha to the membrane of the tympanum. Its 

 commencement is dilated after the form of a funnel, from which 

 the canal grows contracted, and at the farther end is elongated m 

 the direction of the membrane of the tympanum. In composi- 

 tion, it is partly osseous and partly cartilaginous : the auditory 

 process of the petrous portion of the temporal bone constituting 



