34 Arteries of Head and Xcck 



ternal 



Its course in the neck corresponds to that given for the external 

 carotid (p. 23), but in that the external carotid is for the supply of 

 the exterior of the head, whilst the internal carotid is for the brain 

 and the orbit, the internal carotid lies deeper in its ascent. 



The internal carotid takes its strange tortuous course through the 

 petrous bone and through the cavernous sinus in order that the rush 

 of blood from an energetic left ventricle into the delicate cerebral 

 capillaries may be softened down. The same arrangement also 

 obtains in the vertebral arteries in their sub-occipital ascent. 



As the artery passes through the petrous bone it lies just in front 

 of the middle ear, being separated from it by merely a thin osseous 

 plate. It is accompanied by ascending filaments of the cervical sym- 

 pathetic. In certain morbid conditions its pulsations are unpleasantly 

 experienced by the auditory nerve. 



As the artery winds along the inner wall of the cavernous sinus, 

 the sixth nerve rests on its outer side. In the case, therefore, of 

 aneurysm of that part of the artery the external rectus may be 

 weakened or paralysed. Sympathetic filaments surround this part of 

 the artery. 



Branches. A small tympanic twig comes off from the petrosalpart 

 of the artery, and anastomoses with the tympanic branches of the 

 internal maxillary and posterior auricular. 



The ophthalmic, anterior, and posterior cerebral divisions 

 the internal carotid are described on pages 81 and 42. 



The internal jugular vein corresponds to the internal and commoi 

 carotids. 



THE JUGULAR VEINS AND THEIR TRIBUTARI1 

 VEINS OF HEAD AND NECK 



The veins of the interior of the head and of the neck, like thos 

 of the lung, liver, kidney, uterus, and ovary, have no valves. 



The facial vein begins as the angular at the inner corner of the 

 orbit, where it has an important communication with the ophthalmic 

 vein ; it descends obliquely towards the anterior inferior angle of the 

 masseter, lying behind the facial artery, and taking a straighter 

 course. Below the jaw it is joined by a considerable trunk of the tem- 

 poro-maxillary vein ; it continues beneath the platysma and fascia?, 

 and, passing across the external and internal carotids, ends in the 

 internal jugular. It brings down blood from the large median, frontal, 

 and from the supra-orbital veins, and from many tributaries corre- 

 sponding to the branches of the facial artery ; its communications with 

 the ophthalmic vein are of great importance. 



The temporal is formed by the confluence of the superficial 



il and 



