PHARYNX 299 



medial aspects. The cartilage is deficient below and later- 

 ally, its place being taken by dense fibrous tissue, which con- 

 nects 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 side 

 wall of the naso-pharynx (p. 289). A muscular slip, which 

 descends from the lateral margin of the cartilage, in relation 

 to the lateral, unprotected side of the tube, has been termed 

 the dilatator tuba (Rudinger). It joins the tensor of the soft 

 palate. 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 nf tbp nsspnns 

 and cartilaginous parts. As the tube is ^flc^d fmm thp> 

 rsthmuTtO the pharyjlXL it gradually inrrpasps in ralifrrf, anrl it 

 attains its greatest width at its pharyngeal aperture. 



CAROTID CANAL. 



The carotid canal, which traverses the petrous part 

 of the temporal bone, contains the internal carotid artery, 

 the internal carotid continuation of the cervical part of the 

 sympathetic trunk, and a plexus of veins. 



Dissection. To open up the carotid canal, remove its inferior 

 wall with the bone forceps ; but do not interfere with the auditory 

 tube, which lies in close proximity. The dissection must be 

 made on one side only. 



Arteria Carotis Interna. The portion of the internal 

 carotid artery which passes through the carotid canal in the 

 petrous part of the temporal bone is about 18 mm. (three- 

 quarters of an inch) long. At first it ascends vertically; 

 then, bending suddenly, it runs horizontally and forwards. 

 It emerges from the canal at the apex of the petrous 

 bone and enters the foramen lacerum, where it turns upwards, 

 pierces the external layer of the dura mater, and enters 

 the middle fossa of the skull. The remainder of the course 

 of the internal carotid artery has been examined already 

 (p. 239). Within the carotid canal it lies below and anterior 

 to the cochlea and the tympanic cavity. The greater super- 

 ficial petrosal nerve and r the. dteinilunar ganglion are placed 



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