1036 ORGANS OF THE SENSES AND THE COMMON INTEGUMENT 



The arteries of the auricula are the posterior auricular from the external carotid, the anterior 

 auricular from the superficial temporal, and a branch from the occipital artery. 

 The veins accompany the corresponding arteries. 



The sensory nerves are: the great auricular, from the cervical plexus; the auricular branch 

 of the vagus; the auriculotemporal branch of the mandibular nerve; and the lesser occipital 

 from the cervical plexus. 



Cartilage of auricula 

 Attic 

 Incus 



Malleus 



I / Tympanic cavity 

 ' / / Tensor tympani 



I 



Cartilaginous 



part of ext. 

 acoustic meatus 



Tympanic membrane 

 Bony part of 

 ext. acoustic 

 meatus 



FIG. 907. External and middle ear, opened from the front. Right side. 



The External Acoustic Meatus (meatus acusticus externus; external auditory canal 

 .or meatus) extends from the bottom of the concha to the tympanic membrane (Figs. 

 907, 908). It is about 4 cm. in length if measured from the tragus; from the bottom 

 of the concha its length is about 2.5 cm. It forms an 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 inferno). It is an oval cylindrical canal, the greatest diameter 

 being directed downward and backward at the external orifice, but nearly hori- 

 zontally at the inner end. It presents two constrictions, one near the inner end 

 of the cartilaginous portion, and another, the isthmus, in the osseous portion, about 

 2 cm. from the bottom of the concha. The tympanic membrane, which closes the 

 inner end of the meatus, is obliquely directed ; in consequence of this the floor and 

 anterior wall of the meatus are longer than the roof and posterior wall. 



The external acoustic meatus is formed partly by cartilage and membrane, 

 and partly by bone, and is lined by skin. 



The cartilaginous portion (meatus acusticus externus cartilagineus) is about 8 mm. 

 in length; it is continuous with the cartilage of the auricula, and firmly attached 

 to the circumference of the auditory process of the temporal bone. The cartilage 

 is deficient at the upper and back part of the meatus, its place being supplied by 

 fibrous membrane; two or three deep fissures are present in the anterior part of the 

 cartilage. 



The osseous portion (meatus acusticus externus osseus} is about 16 mm. in length, 

 and is narrower than the cartilaginous portion. It is directed inward and a little 



