THE VASCULAR SYSTEM 1 59 



Each carotid artery in the neck region gives off the following 

 branches: an inferior thyreoid to the trachea and oesophagus, a 

 superior thyreoid to the thyreoid 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 vessels 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 continuation 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 superficial temporal branch, turns to 

 pass along the medial 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, sphenopalatine, 

 and infraorbital. 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, sup- 

 plying structures in the orbit, may arise from the carotid 

 plexus or the internal maxillary. The branches of the external 

 maxillary artery are the submental to the symphysis of the 

 lower jaw, and the superior and inferior labial arteries. 



The vertebral artery is the first branch given off by either 

 subclavian. It proceeds dorsad and craniad to the sixth cer- 

 vical vertebra, whence it extends through the transverse for- 

 amina of the cervical vertebrae (vertebrarterial canal) and 

 foramen magnum, to a junction with its fellow in the median 

 line on the ventral aspect of the medulla oblongata. The 

 union of the two vertebral arteries forms the basilar artery, 

 which, after giving off several branches to the medulla and 

 cerebellum, divides craniad of the pons Varolii, forming the 

 circle of Willis around the infundibulum and the optic chiasma 

 at the base of the brain. The circle of Willis receives the 



* The middle meningeal may arise variously, frequently it arises from the 

 intracranial portion of the carotid plexus, Fig. 79 (Norris). 



