408 THE ARTERIES OF THE HEAD AND NECK. 



immediately over the horizontal part of the canal, the roof of which is usually formed 

 for a considerable part of its extent only by fibrous membrane, so that the ganglion 

 comes into close relation \vith the artery. 



WITHIN THE CRANIUM, the internal carotid artery lies in the cavernous sinus as 

 it passes forwards on the side of the body of the sphenoid ; it is surrounded by fila- 

 ments of the sympathetic, the sixth nerve is in contact with its outer side, and it 

 receives, in company with these nerves, an investment from the thin lining membrane 

 of the sinus. Perforating the upper wall of the sinus on the inner side of the 

 anterior clinoid process, the artery ascends between the second and third nerves to 



the anterior perforated spot at the base of 

 the brain, where it divides into its two 

 terminal branches. 



RVE BRANCHES. In the neck the internal 



INT. CAR. ART.-- ^S^JA carotid artery gives usually no branch. While 



in the carotid canal it sends a small offset to 

 the tympanum, which anastomoses with the 

 other tympanic arteries. Within the cavern- 

 ous sinus some small branches proceed from 

 Fig. 343. TRANSVERSE SECTION OP THE it to supply the pituitary body, the Gasserian 

 CAVERNOUS SINUS. (Longer. ) ganglion, the nerves in the outer wall of the 



cavernous sinus, and the adjacent dura mater. 



The last form anastomoses with branches of the meningeal, and recurrent branches 

 of the ophthalmic and lachrymal arteries. Immediately after it has pierced the dura 

 mater, the internal carotid gives off the ophthalmic artery and small twigs to the 

 optic commissure and the beginning of the optic nerve ; and in the vallecula Sylvii, 

 before dividing into the anterior and middle cerebral arteries, it usually furnishes 

 the posterior communicating and the anterior choroid arteries. 



Varieties. The cervical part of this artery is sometimes tortuous. In some very rare 

 cases the internal carotid has arisen directly from the arch of the aorta or from the division 

 of the innominate artery (p. 392). A few examples of its entire absence are recorded. Its 

 lower part occasionally gives origin to the occipital or the ascending pharyngeal artery ; and 

 in one case its intracranial portion furnished a considerable meningeal offset to the posterior 

 fossa of the skull (Curnow). In several instances a large communicating branch has been 

 seen passing from the part of the internal carotid within the cavernous sinus backwards to 

 the trunk of the basilar artery. 



BRANCHES OF THE INTERNAL CAROTID ARTERY. 



1. Ophthalmic artery (v). This artery, arising from the internal carotid on 

 the inner side of the anterior clinoid process, enters the orbit by the optic foramen, 

 below the optic nerve. Having pierce,d the sheath of dura mater, it soon changes 

 its direction, passing round the outer side of, and then over the nerve to reach the 

 inner wall of the orbit, along which it runs forwards between the superior oblique 

 and internal rectus muscles ; and it ends opposite the internal angular process of the 

 frontal bone by dividing into the nasal and frontal arteries. The trunk and 

 branches of the ophthalmic artery are markedly tortuous. 



Branches. (a) The central artery of the retina, a very small vessel, arises close to 

 the optic foramen, as a rule in common with the internal ciliary trunk, less 

 frequently with the external, and seldom independently. About half an inch 

 behind the eyeball it pierces the lower and outer part of the optic nerve, in the 

 centre of which it is then continued to the retina. 



(b) The ciliary arteries are divided into two sets, posterior and anterior. The 

 posterior arise in two chief trunks, an inner and an outer, from the ophthalmic 

 artery while it is below the optic nerve. Each trunk divides into branches (from 3 



