THE INTERNAL EAR. 219 



THE EUSTACHIAN TUBE. 



What is the Eustachian Tube ? It is an osseo- cartilaginous canal, about 

 1% inches long, T ^ inch in diameter at tympanic end, */j inch at pharyngeai, 

 which leads downwards and forwards from the tympanic cavity into the 

 pharynx. Of its length two- thirds is cartilaginous, one-third osseous. Above 

 its bony portion is the canal for the tensor tympani muscle, from which it is 

 Divided by an osseous lamina, the Septum Tuba. Its 



Cartilaginous Portion, consists of two plates of cartilage, their non-ap- 

 proximated edges being connected by a membrane. 

 Pharyngeai Orifice, is trumpet- shaped, and situated in the posterior nasal 



space, just above the nasal floor. 



Mucous Membrane, covered with the ciliated epithelium, and continuous 

 with that of the pharynx and the tympanum. 



Describe the Muscles of the Eustachian Tube. They are the 

 Spheno-salpingo-staphylinus, the abductor or dilator of the tube is described 



as arising from the sphenoid bone and the cartilage of the tube, and being 



inserted into the convex border of the outer cartilage for its whole length. 



Nerve, internal pterygoid. 

 Levator Veli Palati, arises from the temporal bone and the cartilage of the 



tube, into the osseous tube, the cartilage, and the mucous membrane. 



Action, to enlarge the transverse diameter of the tube. Nerve, pneumo- 



gastric. 

 Salpingo-pharyngeus, a thin layer disposed along the median cartilaginous 



plate and the mucous membrane. Action, to fix the median cartilage. 



Called a fascia by some anatomists. 



What Arteries supply the Eustachian Tube ? The 



Ascending Pharyngeai, branch of the external carotid. 



Middlf Meningeal, branch of the internal maxillary br. of the ext. carotid. 



Branch., from the internal carotid artery. 



Name its Nerves. Besides those which supply the muscles of the tube 

 (3ie above), it h?>s branches from the 



Superior Pharyngeai. Glosso-pharyngeal. 



THE INTERNAL EAR. 

 Name the Parts comprised in the Internal Ear. 



Vestibule. 



Osseous Labyrinth, consists of the \ Semicircular Canals. 



Cochlea. 



