THE INTERNAL CAROTID ARTERY. 747 



anticLis major, and having upon its median side the wall of the pharynx and laterally 

 the internal jugular vein, between which and the artery, and on a plane slighdy pos- 

 terior to both, is the pneumogastric nerve. It is also in relation in the upper part 

 of this cervical portion of its course with the glosso-pharyngeal nerve, which lies at 

 first behind it, but crosses its external surface lower down as it bends forward towards 

 the tongue, and with the superior sympathetic ganglion, whose cardiac branch 

 descends along its internal surface, while the pharyngeal branches cross it and 

 the carotid branch ascends with the artery to the carotid canal, in which it breaks 

 up to form the carotid plexus. 



In the second or petrosal portion of its course the internal carotid traverses the 

 carotid canal, to whose direction it conforms, passing at first verticall)' upward and 

 then bendine so as to run forward and inward to enter the cranial cavitv at the 

 foramen lacerum medium. 



It then enters upon the third or intracranial portioji of its course, ascending at 

 first towards the posterior clinoid process, but soon bending forward and entering the 

 outer wall of the cavernous sinus. In this it passes forward, accompanied by the 

 sixth nerve (abducensj, and at the level of the anterior clinoid process bends upward, 

 pierces the dura mater, and quickly divides into its terminal branches. 



Branches. — Throughout its cervical portion the internal carotid normally gives 

 off no branches, in its petrosal portion, in addition to some small twigs to the peri- 

 osteum lining the carotid canal, it gives origin to (i) d. tympanic branch. In its 

 intracranial portion, in addition to small branches to the walls of the cavernous sinus 

 and the related cranial nerves, to the Gasserian ganglion, and to the pituitary body, 

 there arise (2) anterior meningeal branches, (3) \.\\e ophthah?iic, (^\) posterior commu- 

 nicating, (5) ajiterior choroid arteries. And, finally, its terminal branches, (6) the 

 middle and (7) the anterior cerebral arteries. 



Variations. — In its cervical portion the internal carotid occasionally takes a somewhat 

 sinuous course, and, especially in its upper part, may be thrown into a pronounced horseshoe- 

 shaped curve. It may give rise to branches which normally spring from the external carotid, 

 as, for example, the ascending pharyngeal and the lingual, and accessory branches may arise 

 from its intracranial portion. 



Practical Considerations. — The internal carotid artery, on account of its 

 deeper position, is not so often wounded as the external carotid. It has been punc- 

 tured through the pharynx and has been wounded in tonsillotomy (page 1608). 



Aneurism of the internal carotid is not common. When it involves the petrosal 

 or intracranial portion of the vessel it causes symptoms referrible to those regions 

 and better dealt with after the venous system has been described (page 873). In 

 its cervical portion it shows a tendency to become tortuous in elderly persons, 

 owing doubtless to its fixity above, where it enters the carotid canal, and to the rela- 

 tive lack of fixation below (Taylor). 



As the artery is crossed externally by the dense layers of the deep cervical 

 fascia, and by the stylo-hyoid, stylo-glossus, stylo-pharyngeus, and digastric mus- 

 cles, the progress of a swelling in this direction is strongly resisted. Internally the 

 middle constrictor and mucous membrane of the pharynx of!er far less obstruction to 

 the extension of the aneurism, and in many of the recorded cases a pulsating pha- 

 ryngeal protrusion has been the chief symptom. The effects of pressure on surround- 

 ing structures, the internal jugular vein, and the pneumogastric and sympathetic 

 nerves, for example, are not unlike those observed in other carotid aneurisms. The 

 direct interference with cerebral circulation is greater in aneurism of the internal 

 carotid, and vertigo, headache, drowsiness, etc., are apt to be more conspicuous as 

 early symptoms. 



Ligation. — The vessel may be reached close to its origin and tied through the 

 same incision as that used in ligating the external carotid (page 733). The sterno- 

 mastoid muscle is drawn outward, the digastric muscle and hypoglossal nerve 

 (which are usually seen) upward, and the external carotid artery inward. The two 

 vessels should be carefully distinguished. The needle should be passed from with- 



