THE INTRACRANIAL PORTION 



551 



in front of it, by the stj-lo-glossus and stylo-pharyngeus muscles, the glosso-pharyngeal nerve, 

 the pharyngeal branch of the vagus nerve, and by the stylo-hyoid ligament. 



Behind, it Ues upon the longus capitis (rectus capitis anticus major), which separates it 

 from the transverse processes of the three upper cervical vertebrae, on the superior cervical 

 ganglion of the sympathetic nerve, and on the vagus nerve. Near the base of the skull, the 

 hyposlossal, va2;us, glosso-pharyngeal, and spinal accessory nerves cross obhquely behind it, 

 separating it here from the internal jugular vein, which, as the artery is about to 

 enter the carotid canal, also forms one of its posterior relations. 



On its lateral side are the internal jugular vein and vagus nerve. 



On its medial side it is in relation with the pharynx, the superior constrictor muscle separat- 

 ing it from the tonsil. The ascending pharyngeal and ascending palatine arteries, and at the base 

 of the skull the Eustachian tube and levator palati muscles, are also medial to it. 



2. Thf Petrosal Portion 



The petrosal portion (fig. 454) is situated in the carotid canal in the petrous portion of the 

 temporal bone. It is here separated from the walls of the canal by a prolongation downward 

 of the dura mater. In this part of its course it first ascends in front of the tympanum and 

 cochlea of the internal ear; it then turns forward and medially, lying a little medial to and 

 behind the Eustachian tube, and enters the cranial cavity by turning upward through the fora- 



FiG. 454. — The Internal Carotid Artery in the Canal. (After Spalteholz.) 



Superior ophthalmic vein 

 Superficial petrosal branch Cavernous sinus 



Venous plexus 



of internal 



carotid 



Carotico -tympanic 

 branch 



...Jugular fossa 

 ——Longus capitis muscle 

 ——Inferior tympanic artery 

 Internal carotid artery 



Ascending pharyngeal 

 artery 



Atlas 



men lacerum, lying upon the lingula of the sphenoid bone. In this part of its course it is accom- 

 panied by the ascending branches from the superior cervical ganghon of the sympathetic. 

 These form a plexus about the artery, but are situated chiefly on its lateral side. It is also 

 surrounded by a number of small veins, which receive tributaries from the tympanum and open 

 into the cavernous sinus and internal jugular vein. 



3. The Intracranial Portion 



On entering the cranium through the foramen lacerum, the internal carotid first ascends 

 to reach the lateral part of the body of the sphenoid medial to the hngula. It then follows 

 the carotid sulcus forward and slightly downward along the medial wall of the cavernous sinus 

 (fig. 454). Here it has the sixth nerve immediately lateral to it, and is covered by the hning 

 membrane of the sinus. Again turning upward, it pierces the dura mater on the medial side 

 of the anterior chnoid process, and, passes between the second and third nerves to the anterior 

 perforated substance. At the medial end of the lateral (Sylvian) fissure it pierces the arachnoid 

 and divides into its two terminal branches, the anterior and middle cerebral. As it hes in the 



