384 HEAD AND NECK 



canal which conveys air from the pharynx to the tympanic 

 cavity. It is divided into two portions, according to the parts 

 which enter into the construction of its wall. Thus, in the 

 lateral part of its course, as it nears the tympanic cavity, its 

 wall is bony, and it runs in the interval between the tympanic 

 and petrous portions of the temporal bone. The medial part 

 consists mainly of cartilage. It is placed on the base of the 

 skull, and is lodged in the gutter or groove between the 

 petrous part of the temporal bone and the great wing of the 

 sphenoid. This is the subdivision of the tube which comes 

 under the notice of the dissector at the present stage, and 

 he should first note its direction and then study its relations 

 and the construction of its wall. 



The direction of the canal can be readily ascertained by 

 passing a probe into it through its pharyngeal orifice. It runs 

 postero-laterally with a slight inclination upwards and passes 

 first above and then to the lateral side of the levator palati, 

 and along the medial side of the upper part of the tensor palati. 

 It lies, therefore, in a considerable part of its extent between 

 the two muscles. 



Before removing the mucous membrane from the 

 pharyngeal part of the tube the dissector should note that at 

 the lower margin of the orifice there is a prominent rounded 

 eminence, the levator cushion^ due to the subjacent levator veli 

 palatini. The removal of the mucous membrane will reveal the 

 fact that the wall of the tube is formed, in great part, by a 

 triangular plate of cartilage, which is folded upon itself so 

 as to protect the tube on its upper and medial aspects. The 

 cartilage is deficient below and laterally, its place being 

 taken by dense fibrous tissue, which connects the margins 

 of the cartilage and completes the wall of the canal. The 

 projecting free base of the cartilage gives rise to the torus 

 tubarius already examined on the lateral wall of the naso- 

 pharynx (p. 376). A muscular slip, which descends from the 

 lateral margin of the cartilage, in relation to the outer un- 

 protected side of the tube, has been termed the dilatator tuba 

 (Rudinger). It joins the tensor palati. The interior of the 

 tube is lined with mucous membrane continuous with that 

 of the pharynx and the tympanic cavity ; and its calibre varies 

 considerably in different parts of its course. It is narrowest 

 at a point termed the isthmus, situated at the junction of 

 the osseous and cartilaginous parts. As the tube is traced 



