198 CIRCULATOR V SYSTEM. 



The Carotid having got as high as the space between the os 

 hyoides and the thyroid cartilage, but varying slightly in differ- 

 ent subjects, there divides into two large trunks, the Internal 

 Carotid, which goes to the brain and to the eye; and the Exter- 

 nal Carotid, which is principally distributed upon the more su- 

 perficial parts of the head and neck. The first of these trunks 

 is placed behind the other, and bends outwardly at its root : it is 

 generally the largest in infancy, on account of the proportionate 

 volume of the brain at that age; it is also swollen at its root, so 

 as to form a sinus there, resembling an incipient aneurism. No 

 branch, except in the abnormous cases, is given off from the*con> 

 mon carotid between its origin and bifurcation, 



SECT. II. OP THE CAROTIDS, AND THEIR BRANCHES. 



The Internal Carotid. (Arteria Carotis Internet,) in the adult, 

 is smaller than the external, and extends from the larynx to the 

 sella turcica. It ascends between the external carotid and the 

 vertebra of the neck, being in front of the internal jugular vein, 

 and having the pneumogastric nerve at its outer margin: as it 

 gets on a level with the base of the lower jaw, it is crossed ex- 

 ternally by the digastric and the stylo-hyoid muscles: it is im- 

 mediately afterwards concealed in the subsequent part of its 

 ascent by the ramus of the lower jaw. Having gone along the 

 most internal or deeply seated margin of the parotid gland and 

 the styloid process of the temporal bone, at the side of the supe- 

 rior constrictor of the pharynx, it then penetrates into the crani- 

 um through the carotid canal of the temporal bone. 



It is slightly flexed between its origin and the carotid canal : 

 just before it reaches the latter, it curves upwards and forwards. 

 The first part of its course through the canal is vertical, after- 

 wards it goes horizontally forwards; and to escape from the ca- 

 nal it has once more to ascend almost vertically, which brings 

 it to the posterior extremity of the Selhi Turcica, On the side 

 of the Sella Turcica it again passes horizontally forwards through 

 the cavernous sinus; and at the anterior clinoid process it once 

 more ascends, and, having penetrated the dura mater, it reaches 

 the brain. 



In this passage, through the carotid canal, it is attended by 



