260 INTERNAL CAROTID ARTERY. 



The carotid canal in the petrous portion of the temporal bone 

 is by no means straight ; it forms a semicircular curve, forwards 

 and inwards; and its upper portion, which is nearly horizontal, 

 opens obliquely against the body of the sphenoid bone, at a 

 small distance from it. Therefore, after the artery has passed 

 through the canal, it must turn upwards to get fairly into the 

 cavity of the cranium ; and, of course, its direction while in the 

 canal, forms almost a right angle with its direction before it 

 enters, and after it emerges from it. 



In consequence of this curvature, much of the momentum of 

 the blood must be impressed upon the walls of the cranium, and 

 is thus taken off from the brain, so as not to disturb the action 

 of its delicate structure. 



After the artery has arrived at the end of the carotid canal, 

 and has turned upwards to get within the cavity of the cranium, 

 it bends forwards, and passes nearly in a horizontal direction, 

 through the cavernous sinus on the side of the sella turcica, to 

 the anterior clinoid process ; here it again forms a considerable 

 curve, which is directly upwards, and then it perforates the 

 dura mater. 



These curvatures must also deprive the blood of the carotid of 

 a portion of the momentum which it has retained after leaving 

 the bone. 



The object of these various flexures of the internal carotid 

 appears to be analogous to that of the Rete Mirabile in certain 

 quadrupeds, which is formed by the division of this artery 

 into many small branches, that reunite again, without pro- 

 ducing any other effect than the diminution of the momentum 

 of the blood. 



During its course from the place of bifurcation to its entrance 

 into the carotid canal, the internal carotid artery very rarely 

 sends off any branches. In the canal it gives off a small twig 

 which enters ' the cavity of the tympanum ; and sometimes a 

 second, which unites with the Pterygoid branch of the internal 

 maxillary. 



As it goes by the sella turcica, it passes through the 

 cavernous sinuses, and gives off two branches, which are 



