CAROTID CANAL 385 



thence to the pharynx it gradually increases in calibre, and it 

 attains its/ greatest width at its opening into the naso-pharynx. 



CAROTID CANAL. 



The carotid canal, which traverses the interior of the 

 petrous part of the temporal bone, contains the internal 

 carotid artery, the internal carotid continuation of the cervical 

 sympathetic and a plexus of veins. 



Dissection. -The carotid canal may be opened up by removing its 

 inferior wall with the bone forceps. In doing this, it is not necessary to 

 interfere with the auditory tube, which lies in close proximity. The dis- 

 section must be made on one side only. 



Arteria Carotis Interna. The internal carotid artery in 

 this part of its course is about three-quarters of an inch long. 

 At first it ascends vertically ; then, bending suddenly, it runs 

 horizontally antero-medially. 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. From this 

 point onwards the internal carotid artery has been examined 

 already (p. 331). Whilst within the carotid canal it lies 

 below and anterior to the cochlea and the tympanic cavity. 

 The great superficial petrosal nerve and the semilunar 

 ganglion are placed above it, but are separated from it by a 

 thin plate of bone, which is, however, sometimes absent. 



Nervus Caroticus Interims. The dissector has already 

 noted this large branch proceeding from the upper end of 

 the superior cervical ganglion and entering the carotid canal 

 with the internal carotid artery. It divides almost im- 

 mediately into two parts, which are placed on either side of 

 the artery. Each of these soon divides into a number of 

 branches which communicate together around the internal 

 carotid artery forming the internal carotid plexus. The 

 further dissection of these branches is a matter of some 

 difficulty, and can be satisfactorily effected only under 

 specially favourable circumstances. 



At the posterior end of the cavernous sinus a ganglion is sometimes 



found in the plexus, and where the sixth nerve crosses the internal carotid 



artery the plexus is very dense. This part is known as the cavernous 



plexus. At the anterior end of the cavernous sinus the carotid plexus 



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