1124 



THE ORGANS OF SPECIAL SENSE 



lymphatics enter into the preauricular nodes and the nodes upon the Sternomastoid muscle 

 at its insertion. The nerves of the pinna are the great auricular, from the cervical plexus; 

 the auricular branch of the vagus; the auriculotemporal branch of the inferior maxillary nerve; 

 the small occipital from the cervical plexus, and the great occipital or internal branch of the 

 dorsal division of the second cervical nerve. The muscles of the pinna are supplied by the 

 facial nerve. ,_ 



The Auditory Canal, or MeatUS (meatus acusticus externus), extends from the 

 bottom of the concha to the membrana tympani (Figs. 833 and 834). It is about 

 3.7 cm. (an inch and an half) in length if measured from the tragus ; from the bottom 

 of the concha its length is about 2.5 cm. (an inch). It forms a sort of S-shaped 

 curve, and is directed at first inward, forward, and slightly upward (pars externa) ; 

 it then passes inward and backward (pars media}, and lastly is "carried inward, 

 forward, and slightly downward (pars inter no). It forms an oval cylindrical 



Promont. 



Int. carot. a. 



Cartilage of the cxt. 

 auditory meatus 



FIG. 833. Transverse section of external auditory meatus and 

 tympanum. Leftside. (Gegenbaur.) 



canal, the greatest diameter being in the vertical direction at the external orifice, 



but in the transverse direction 

 at the tympanic end. It pre- 

 sents two constrictions, one 

 near the inner end of thp rarh'- 

 laginous portion, and another, 

 the isthmus, in the osseous 

 portion, about 2 cm. (three- 

 quarters of an inch) from the 

 bottom of the concha. The 

 membrana tympani (Figs. 833 

 and 834), which closes the 

 inner end of the meatus, is 

 directed obliquely, in conse- 

 quence of which the floor of 

 the canal is longer than the 

 roof, and the anterior wall 

 longer than the posterior. 

 The auditory canal is formed 

 partly by cartilage and membrane, partly by bone, and is lined by perichondrium 

 and periosteum, which is covered with skin. 



The cartilaginous portion (meatus acusticus externus cartilagineus) is about 

 8 mm. (one-third of an inch) in length; it is formed by the cartilage of the pinna, 

 prolonged inward, and firmly attached to a greater portion of the circumference 

 of the auditory process of the temporal bone. The cartilage is deficient at its 

 upper and back part, its place being supplied by a fibrous membrane. This 

 part of the canal is rendered extremely movable by two or three deep fissures, the 

 fissures of Santorini (incisurae cartilaginis meatus acustici externi [Santorini]), 

 which extend through the cartilage in a vertical direction. 



The osseous portion (meatus acusticus externus osseus) is about 16 mm. (two- 

 thirds of an inch) in length, and narrower than the cartilaginous portion. It is 

 directed inward and a little forward, forming a slight curve in its course, the con- 

 vexity of which is upward and backward. Its inner end, which communicates, 

 in the dry bone, with the cavity of the tympanum, is smaller than the outer and 

 sloped, the anterior w f all projecting beyond the posterior about 4 mm. (one-sixth 

 of an inch); it is marked, except at its upper part, by a narrow groove, the tympanic 

 sulcus (sulcus tympanicus), in which the circumferential margin of the membrana 

 tympani is attached. Its outer edge is dilated and rough in the greater part of 

 its circumference, for the attachment of the cartilage of the pinna. Its transverse 

 section is oval, the greatest diameter being from above downward and backward. 

 The front and lower parts of this canal are formed by a curved plate of bone, 



