256 THE VASCULAR SYSTEMS 



For description it is divided into four parts ; the first, or cervical, 

 extends from the bifurcation of the common carotid to the caro- 

 tid canal; the second, or petrous, is in the carotid canal; the 

 third, or cavernous, runs in the cavernous sinus; and the fourth, 

 or cerebral, is the terminal portion. 



Relations. Cervical portion in front, external carotid artery 

 and its occipital and posterior auricular branches; hypoglossal, 

 glossopharyngeal nerves, and pharyngeal branch of the vagus; 

 behind, rectus capitis anticus major, sympathetic and superior 

 laryngeal nerves; externally, s ^ m an ^ fascise, sternomastoid, 

 digastric, and the styloid process with its muscles, internal 

 jugular vein and vagus, both being in the same sheath with the 

 artery, but having each a separate investment, the nerve being 

 posterior to, and between, the artery and vein. Near the base 

 of the skull the spinal accessory, glossopharyngeal, the vagus, 

 and hypoglossal nerves emerge between the vein and artery. 

 Internally the pharynx and tonsil, ascending pharyngeal artery, 

 superior and external laryngeal nerves. 



The petrous portion- is at first in front of the tympanum and 

 internal ear, and then runs forward and inward to the inner 

 side of the foramen lacerum medium, and ascends, accompanied 

 by the sympathetic, to the cavernous sinus. 



The cavernous portion, lies on the floor of the sinus, surrounded 

 by the sympathetic, the sixth nerve being external. 



The cerebral portion pierces the dura mater internal to the 

 anterior clinoid process, lying at the inner extremity of the 

 Sylvian fissure, between the second and third nerves. 



The Branches of the Internal Carotid Artery. The first portion 

 gives no branches. The second sends a tympanic branch through 

 a foramen in the carotid canal. The third gives off the arterias 

 receptaculi to the pituitary gland, Gasserian ganglion, the 

 cavernous and inferior petrosal sinuses. One of these branches 

 is the anterior meningeal. It also gives off the ophthalmic. 



The ophthalmic artery passes through the optic foramen, 

 below and external to the nerve, then crosses the latter, and 

 runs beneath the superior oblique muscle to the inner angle 

 of the eye, and divides into the frontal and nasal; It gives off 

 two sets of branches, viz., orbital and ocular. 



The ORBITAL branches are the following: 



(a) The lurry mal runs above the external rectus to the 

 gland, sending several malar branches through the bone to the 



