386 ARTERIES. 



After ascending in it for a short distance, it passes forwards and inwards through 

 the carotid canal, and, ascending a little by the side of the sella Turcica, curves 

 upwards by the anterior clinoid process, where it pierces the dura mater, and 

 divides into its terminal branches. 



This vessel supplies the anterior part of the brain, the eye, and its appendages. 

 Its size, in the adult, is equal to that of the external carotid. In the child, it is 

 larger than that vessel. It is remarkable for the number of curvatures that it 

 presents in different parts of its course. In its cervical portion it occasionally pre- 

 sents one or two flexures near the base of the skull, whilst through the rest of its 

 extent it describes a double curvature, which resembles the italic letter / placed 

 horizontally *->. These curvatures most probably diminish the velocity of the 

 current of blood, by increasing the extent of surface over which it moves, and 

 adding to the amount of impediment produced from friction. In considering the 

 course and relations of this vessel, it may be conveniently divided into four por- 

 tions, a cervical, petrous, cavernous, and cerebral. 



Cervical Portion. This portion of the internal carotid at its commencement is 

 very superficial, being contained in the superior carotid triangle, on the same level 

 as, but behind, the external carotid, overlapped by the Sterno-mastoid, and covered 

 by the Platysma, deep fascia, and integument ; it then passes beneath the parotid 

 gland, being crossed by the hypoglossal nerve, the Digastric and Stylo-hyoid 

 muscles, and the external carotid and occipital arteries. Higher up, it is separated 

 from the external carotid by the Stylo-glossus and Stylo-pharyngeus muscles, the 

 glosso-pharyngeal nerve, and pharyngeal branch of the vagus. It is in relation, 

 lehind, with the Rectus anticus major, the superior cervical ganglion of the 

 sympathetic, and superior laryngeal nerve ; externally, with the internal jugular 

 vein, and pueumogastric nerve ; internally, with the pharynx, tonsil, and ascend- 

 ing pharyngeal artery. 



Petrous Portion. When the internal carotid artery enters the canal in the 

 petrous portion of the temporal bone, it first ascends a short distance, then curves 

 forwards and inwards, and again ascends as it leaves the canal to enter the cavity 

 of the skull. In this canal, the artery lies at first anterior to the tympanum, 

 from which it is separated by a thin bony lamella, which is cribriform in the 

 young subject, and often absorbed in old age. It is separated from the bony wall 

 of the carotid canal by a prolongation of dura mater, and is surrounded by fila- 

 ments of the carotid plexus. 



Cavernous Portion. The internal carotid artery, in this part of its course, at first 

 ascends to the posterior clinoid process, then passes forwards by the side of the 

 body of the sphenoid bone, being situated on the inner wall of the cavernous 

 sinus, in relation, externally, with the sixth nerve, and covered by the lining 

 membrane of the sinus. The third, fourth, and ophthalmic nerves are placed on 

 the outer wall of the sinus, being separated from its cavity by the lining membrane. 



Cerebral Portion. On the inner side of the anterior clinoid process the internal 

 carotid curves upwards, perforates the dura mater bounding the sinus, and is 

 received into a sheath of the arachnoid. This portion of the artery is on the 

 outer side of the optic nerve; it lies at the inner extremity of the fissure of 

 Sylvius, having the third nerve externally. 



Peculiarities. The length of the internal carotid varies according to the length of the neck, 

 and also according to the point of bifurcation of the common carotid. Its origin sometimes 

 takes place from the arch of the aorta ; in such rare instances, this vessel was placed nearer the 

 middle line of the neck than the external carotid, as far upwards as the larynx, when the latter 

 vessel crossed the internal carotid. The course of the vessel, instead of being straight, may be 

 very tortuous. A few instances are recorded in which this vessel was altogether absent : in one 

 of these the common carotid ascended the neck, and gave off the usual branches of the external 

 carotid, the cranial portion of the vessel being replaced by two branches of the internal maxil- 

 lary, which entered the skull through the foramen rotundum and foramen ovale, and joined to form 

 a single vessel. 



Surgical Anatomy. The cervical part of the internal carotid is sometimes wounded by a stab 

 or gunshot wound in the neck, or even occasionally by a stab from within the mouth, as when 



