THE VASCULAR SYSTEM. 147 



brachiocephalic, which is then continued as the right 

 subclavian. In this case the common trunk of the ca- 

 rotid usually bifurcates within one or two centimeters of 

 its origin, forming the right common carotid and the 

 left common carotid, lying on the respective sides of the 

 trachea beneath the sternomastoid and the sternohyoid 

 muscles. The vagus or tenth cranial nerve and the 

 sympathetic trunk lie in the same sheath with the 

 carotid (Fig. 64). 



Each carotid artery in the neck region gives off the 

 following branches : a thyroid to the thyroid cartilage and 

 gland, and a muscular to the muscles of the neck. At 

 the base of the skull, about the middle of the bulla of 

 the temporal bone, a slight enlargement of the vessel is 

 seen, from which arises the very small internal carotid, 

 leading through the foramen lacerum medius to the base 

 of the brain, where it joins the circle of Willis. The con- 

 tinuation of the common carotid is now known as the 

 external carotid. This, after giving off a lingual branch 

 to the tongue, an external maxillary branch to the lower 

 jaw, a post-auricular branch, and a temporal branch, 

 turns to pass along the mesal aspect of the mandible, 

 where it is named the internal maxillary, whose main 

 branches are the inferior alveolar, the middle meningeal 

 supplying the dura mater, several branches to form the 

 carotid plexus, a palatine, spheno palatine, and infraor- 

 bital. The latter is the direct continuation of the internal 

 maxillary. It supplies the upper teeth, lower eyelid, 

 parts of the nose, and upper lip. An ophthalmic branch, 

 supplying structures in the orbit, may arise from the 

 carotid plexus or the internal maxillary. 



The -vertebral artery is the first branch given off by 

 either subclavian. It proceeds dorsad and cephalad to 

 the sixth cervical vertebra, whence it extends through 



