THE EUSTACHIAN TUBE. 



87 



cartilaginous part than in the osseous. The posterior or osseous division of the 

 tube, about half an inch long, is placed at the angle of junction of the petrous 

 portion of the temporal bone with the squamous portion. It is funnel shaped, 

 diminishing somewhat rapidly in size from behind forwards, to the junction with 

 the cartilaginous part ; here the tube is narrowest (isthmus tubce). The carotid 

 canal lies mesially to the osseous portion of the tube, and is occasionally found to 

 communicate with it owing to deficiencies in the bony septum between them. 



The mucous membrane lining the osseous portion of the tube is thin and closely 

 attached to the bone except along the floor of the canal, where it is separated from the 

 periosteum by a venous plexus. It is lined by ciliated epithelium, and has no glands 

 opening into it. The anterior part of the tube, about an inch in length, is formed of a 

 triangular piece of elastic fibro-cartilage, the edges of which are slightly curled 

 round towards each other, leaving an interval at the under and outer side, in which the 

 wall of the canal is completed by dense but pliable fibrous membrane (fascia salpingo- 

 pharyngea), and by a muscular band connected with the tensor palati and termed by 



Fig. 95. SECTION ACROSS THE CARTILA- 

 GINOUS PART OF THE EUSTACHIAN 

 TUBE. (Riidinger.) 



1, 2, bent cartilaginous plate; 3, 

 muse, dilatator ttibse ; to the left of 4, 

 part of the attachment of the levator palati 

 muscle ; 5, tissue uniting the tube to the 

 base of the skull ; 6, and 7, mucous 

 glands ; 8, 10, fat ; 9 to 11, lumen of the 

 tube ; 12, connective tissue on the lateral 

 aspect of the tube. 



Riidinger the dilatator tula. The 

 cartilaginous plate is hook-shaped 

 in transverse section (fig. 95), the 

 larger part of the plate being on 

 the mesial side, and only a small 

 part on the lateral border. The 

 cartilage is largest near the ostium 

 pharyngeum, where it measures 

 12 mm. from above down, and is 



7 mm. thick. It here occupies the whole mesial wall of the tube, but gradually 

 diminishes in size as it approaches the bony canal. It is often partially or entirely 

 broken up by fissures, or there may be accessory pieces of cartilage in various 

 situations in the wall of the tube. The cartilaginous part of the tube is trumpet- 

 shaped, being narrow behind, and gradually expanding to a greater width in 

 front (fig. 1)4) ; the anterior part is compressed from side to side, and is fixed 

 to the inner pterygoid plate of the sphenoid bone. The anterior opening (ostium 

 pharyngeum) is of a compressed oval, somewhat triangular form, and is placed 

 obliquely at the side and upper part of the pharynx, into which its prominent 

 margin projects behind the lower turbinate process of the nose and above the level 

 of the hard palate (fig. 96). The aperture is bounded above and posteriorly by a 

 projection, which is caused by the end of the curved plate of cartilage (covered, 

 of course, by mucous membrane), which separates it behind from a longitudinal 

 depression of the pharyngeal wall, known as the lateral recess of the pharynx or 

 fossa of Rosenmiiller. The projection in question is continued into the salpingo- 

 pharyngeal fold. Below it is limited by a thickening, increased when the 

 levator palati contracts, continued from a fold (salpingo-palatine), which also 

 assists in forming the anterior boundary of the orifice. The opening is placed 



