THE INTERNAL CAROTID ARTERY 611 



the skull between the lingula and petrosal process. In this canal the artery lies 

 at first in front of the cochlea and tympanum; from the latter cavity it is separated 

 by a thin, bony lamella. Farther forwarl it is separated from the Gasserian 

 ganglion by a thin plate of bone, which forms the floor of the fossa for the ganglion 

 and the roof of the horizontal portion of the canal. Frequently this bony plate 

 is more or less deficient, and then the ganglion is separated from the artery by a 

 fibrous membrane. The artery is separated from the bony wall of the carotid 

 canal by a prolongation of the dura, and is surrounded by a number of small veins 

 and by filaments of the carotid plexus, derived from the ascending branch of the 

 superior cervical ganglion of the sympathetic. 



Cavernous Portion. The internal carotid artery in this part of its course is 

 situated between the layers of the dura forming the cavernous sinus, but is covered 



Mby the lining membrane of the sinus. It at first ascends to the posterior clinoid 

 process, then passes forward by the side of the body of the sphenoid bone, and 

 again curves upward on the inner side of the anterior clinoid process, and per- 



. forates the dura, forming the roof of the sinus. In this part of its course it is 

 surrounded by filaments of the sympathetic nerve, and has in relation with it 

 externally the abducent nerve. * 



Cerebral Portion. Having perforated the dura, on the inner side of the anterior 



< clinoid process, the internal carotid passes between the optic and oculomotor 

 nerves to the anterior perforated substance at the inner extremity of the sylvian 

 fissure, where it gives off its terminal or cerebral branches. This portion of the 

 artery has the optic nerve on its inner side, and the oculomotor nerve externally. 



Peculiarities. The length of the internal carotid varies according to the length of the neck, 

 and also according to the point of bifurcation of the common carotid. Its origin sometimes 

 takes place from the arch of the aorta; in such rare instances this vessel has been found to be 

 placed nearer the middle line of the neck than the external carotid, as far upward as the larynx, 

 when the latter vessel crossed the internal carotid. The course of the vessel, instead of being 

 straight, may be very tortuous. A few instances are recorded in which this vessel was altogether 

 absent; in one of these the common carotid passed up the neck, and gave off the usual branches 

 of the external carotid, the cranial portion of the internal carotid being replaced by two branches 

 of the internal maxillary, which entered the skull through the foramen rotundum and the foramen 

 ovale and joined to form a single vessel. 



Applied Anatomy. The cervical part of the internal carotid is very rarely wounded. Mr. 

 Cripps, in an interesting paper in the Medico-Chirurgical Transactions, compares the rareness 

 of a wound of the internal carotid with one of the external carotid or its branches. It is, however, 

 sometimes injured by a stab or gunshot wound in the neck, or even occasionally by a stab from 

 within the mouth, as when a person receives a thrust from the end of a parasol or falls down 

 with a tobacco-pipe in his mouth. It used to be believed that the internal carotid was occa- 

 sionally wounded in the removal of the tonsil. Such an accident cannot happen if the artery is 

 normally placed. The severe and sometimes fatal hemorrhage which has followed this oper- 

 atian in a few instances probably had as its source enlarged branches of the ascending pharyn- 

 geal, tonsillar, or ascending palatine arteries. Recently, however, Dr. Gwilym G. Davis, of 

 Philadelphia, demonstrated a specimen in which the internal carotid could have been wounded 

 by incision of the tonsil. The indications for ligation are wounds, when the vessel should be 

 exposed by a careful dissection and tied above and below the bleeding point; and aneurism, 

 which if non-traumatic may be treated by ligation of the common carotid, but if traumatic in 

 origin by exposing the sac and tying the vessel above and below. The incision for ligation of 

 the cervical portion of the internal carotid should be made along the anterior border of the 

 Sternomastoid, from the angle of the mandible to the upper border of the thyroid cartilage. The 

 superficial structures being divided and the Sternomastoid defined and drawn outward, the 

 cellular tissue must be carefully separated and the posterior belly of the Digastric muscle and 

 the hypoglossal nerve sought for as guides to the vessel. When the artery is found the external 

 carotid should be drawn imvard and the Digastric muscles upward, and the aneurism needle 

 passed from without inward. 



Obstruction of the internal carotid by embolism or thrombosis may give rise to symptoms of 

 cerebral anemia and softening if the collateral circulation is ill-developed. The patient suffers 

 from giddiness, with failure of mental powers, and convulsions, coma, or hemiplegia on the 

 opposite side of the body, may be observed. 



