DISSECTION OF THE HEAD AND NECK 



385 



External Acoustic Meatus (Meatus acusticus externus). 



Examine the external acoustic meatus (meatus acusticus ex- 

 ternus) thus opened, and compare it with a dry temporal bone, 

 and if possible with a macerated specimen showing the carti- 

 laginous part well. Study 



(a) External acoustic porus (porus acusticus externus). 



(b) Tympanic incisure (incisura tympanica [Eivini}). 



(c) Cartilaginous external acoustic meatus (meatus acusticus externus 



cartilagineus) . 



(d) Cartilage of acoustic meatus (cartilago meatus acustici). 



(da) Notches in cartilage of external meatus (incisurae cartilagi- 



nis meatus acustici externi [Santorini]). 



(db) Layer of tragus (lamina tragi). 



FIG. 186. 



Incus 



Canalis semicircularis lateralis 

 Canalis semicircularis superior 

 Vestibulum labyrinthi 



/ 



Basis stapedis 



/ Apertura vestibularis cochleae 



Area vestibula- 

 ris superior 



.Grista trans- 



Meatus acus- 

 ticus exter- 

 nus 



s Tractusspiralisforaminosus 

 Cochlea (scala tympani) 



Lamina spirnlis (ossea and 

 membranacea ) 



I Jlulbus V. jugularis supcric 



Membrana tympani Cavum tymp'an'i 



Nearly frontal section through the outer, middle, and inner ear. (After Toldt, Anat. Atlas, 

 Wien, 1903, 3 Aufl., p. 932, Fig. 1447.) 



Cavity of Tympanum (Cavum tympani). 



This cavity (cavum tympani) should next be studied. Make 

 an opening through the roof of the tympanum (tegmen tympani) 

 just lateral from the eminentia arcuata (due to the superior 

 semicircular canal) and about one centimetre in front of the 

 angulus superior pyramidis. The opening leads into the tym- 

 panic antrum of the mastoid wall of the cavity of the tympanum. 

 Enlarge the opening carefully with bone-forceps, gradually re- 

 moving piece by piece the whole roof or tegmental wall (paries 



25 



