THE INTERNAL CAROTID ARTERY. 407 



inferior dental and posterior deep temporal arteries arise is often continued forwards over the 

 external pterygoid by means of a muscular and anastomotic branch, to join the anterior deep 

 temporal or buccal, thus affording an indication of the manner in which the superficial course 

 has been acquired. 



The number of branches arising from the internal maxillary artery is frequently reduced 

 owing to two or more taking origin by a common trunk. The middle meningeal artery 

 occasionally furnishes the lachrymal, or even the ophthalmic artery itself ; and on the other 

 hand the ophthalmic has been seen to give off the middle meningeal, peculiarities which may 

 be explained as resulting from the enlargement of the ordinary anastomosing branch. The 

 anterior deep temporal artery may reinforce or replace the lachrymal artery by a similar 

 enlargement of an anastomosing branch. The buccal, posterior dental, oxj/tifraorbital artery 

 may be larger than usual, supplying a deficiency of the facial artery. 



INTERNAL CAROTID ARTERY (II). 



COURSE AND RELATIONS. The internal carotid artery is distributed to the brain, 

 to the eye with its appendages, and in part to the forehead and nose. It extends 

 directly upwards ^from the termination of the common carotid artery, just above 

 the thyroid cartilage, to the carotid canal of the temporal bone. Traversing this 

 canal, it enters the cranial cavity by the inner part of the foramen lacerum, and 

 then passes forwards in the carotid groove on the side of the body of the sphenoid 

 bone, at the fore part of which it makes a sharp bend with its convexity directed 

 forwards. Lastly, it turns upwards on the inner side of the anterior clinoid process 

 to reach the vallecula Sylvii at the inner end of the Sylvian fissure of the brain, 

 where it terminates by dividing into the anterior and middle cerebral arteries. 



IN THE NECK, the internal carotid artery lies at first behind the external carotid, 

 and is covered only by the sterno-mastoid muscle with the platysma myoides and 

 fascia. It soon, however, passes beneath the digastric and stylo-hyoid muscles, 

 gaining the inner side of the external carotid trunk, and is then deeply placed 

 beneath the parotid gland, the styloid process and the stylo-pharyngeus muscle. 

 Behind the artery are the vertebrse covered by the rectus anticus major muscle, and 

 on its inner side is the pharynx. The internal jugular vein is in contact with the 

 artery as far as the base of the skull, lying on its outer and posterior aspect, and the 

 two are enclosed, together with the pneumo- gas trie nerve, in a prolongation of the 

 carotid sheath. The vessel is crossed by the occipital artery beneath the digastric, 

 and by the posterior auricular artery above that muscle. The pneumo-gastric nerve 

 and the upper cervical ganglion of the sympathetic are placed deeply behind the 

 artery ; the hypoglossal nerve crosses it superficially near the lower border of the 

 digastric, and higher up the glosso-pharyngeal nerve and the phanjngeal branch of 

 the pneumo-gastric pass forwards between the external and internal carotids ; while 

 the superior and external laryngeal nerves are internal to both vessels. Close to the 

 base of the skull the glosso-pharyngeal, pneumo-gastric, spinal accessory and hypo- 

 glossal nerves issue between the artery and its companion vein. 



IN THE CAROTID CANAL, the artery first ascends for a short distance, being placed 

 immediately in front of the tympanum and the cochlea of the internal ear, and then 

 passes horizontally forwards and inwards to the foramen lacerum, where it turns up- 

 wards in the groove of the sphenoid between the lingula and the petrosal process. It 

 is here accompanied by the ascending branch of the upper cervical ganglion of the sym- 

 pathetic, and surrounded by a venous plexus. The bend formed by the artery within 

 the carotid canal is crossed on the outer side by the Eustachian tube ; and not 

 unfrequently it extends backwards beneath the lower and fore part of the inner wall 

 of the tympanum, being separated from that cavity only by a thin plate of bone, 

 which may even be deficient in part. 1 Farther forwards, the Gasserian ganglion lies 



1 W. Anderson, " The Relation of the Internal Carotid Artery to the Inner Wall of the Tympanum," 

 Thomas's Hospital Reports, xix. 



