THE INTERNAL CAROTID ARTERY. 503 



carotid triangle, and lying on the same level as the external carotid, but behind 

 that artery overlapped by the Sterno-mastoid and covered by the deep fascia, 

 Platysma, and integument : it then passes beneath the parotid gland, being crossed 

 by the hypoglossal nerve, the Digastric and Stylo-hyoid muscles, and the occipital 

 and posterior auricular arteries. Higher up, it is separated from the external 

 carotid by the Stylo-glossus and Stylo-pharyngeus muscles, the glossopharyngeal 

 nerve, and pharyngeal branch of the pneumogastric. It is in relation, behind, with 

 the Rectus capitis anticus major, the superior cervical ganglion of the sympathetic, 

 and superior laryngcal nerve ; externally, with the internal jugular vein and pneu- 

 mogastric nerve, the nerve lying on a plane posterior to the artery ; internally, 

 with the pharynx, tonsil, the superior laryngeal nerve, and ascending pharyngeal 

 artery. At the base of the skull the glosso-pharyngeal, vagus, spinal accessory, 

 and hypoglossal nerves lie between the artery and the internal jugular vein. 



PLAN or THE RELATIONS OF THE INTERNAL CAROTID ARTERY IN THE NECK. 



In front. 



Skin, superficial and deep fasciae. 

 Platysma. 

 Sterno-mastoid. 



Occipital and posterior auricular arteries. 

 Hypoglossal nerve. 

 Parotid gland. 



Stylo-glossus and Stylo-pharyngeus muscles. 

 Glosso-pharyngeal nerve. 

 Pharyngeal branch of the pneumogastric. 



Externally. Intenu **' 



I CaS Pharynx. 



Internal jugular vein. I Arte ry. / Superior laryngeal nerve. 



Pneumogastric nerve. Ascending pharyngeal artery. 



Tonsil. 

 Behind. 



Rectus capitis anticus major. 

 Sympathetic. 

 Superior laryngeal nerve. 



Petrous Portion. When the internal carotid artery enters the canal in the 

 petrous portion of the temporal bone, it first ascends a short distance, then curves 

 forward and inward, and again ascends as it leaves the canal to enter the cavity of 

 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, which is cribriform in the young subject, and often ab- 

 sorbed in old age. Farther forward 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 fibrous 

 membrane. The artery is separated from the bony wall of the carotid canal by a 

 prolongation of dura mater, and is surrounded by filaments of the carotid plexus, 

 derived from the ascending branch of the superior cervical ganglion of the sympa- 

 thetic, and a number of small veins. 



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

 situated between the layers of the dura mater forming the cavernous sinus, but 

 covered by 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 

 perforates the dura mater, 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 sixth nerve. 



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

 anterior clinoid process, the internal carotid passes between the second and third 



