THE COMMON CAROTID ARTERIES. 667 



left, on the internal face of the hemispheres, a short distance from the corpus 

 callosum, and near the posterior extremity of that great commissure. The 

 branches emitted by these arteries — either in their track or at their termination — 

 anastomose with those of the posterior and middle cerebral arteries, as well as 

 with the lobular branch of the o])hthalmic. 



Before uniting in a common trunk, the two anterior cerebral arteries receive 

 the meningeal branch of the ophthalmic, the calibre of which often even sur- 

 passes that of these vessels. 



From the anastomosis of the anterior cerebral arteries and the posterior 

 cerebral with the terminal branches of the basilar artery, there results on the 

 inferior surface of the pons Varolii an irregular arterial circle — the circle or 

 polygon of Willis, which surrounds the pituitary gland. From this circle are 

 detached six groups of arterioles, which are destined to supply the principal grey 

 masses in the brain — the corpus striatum and optic thalami. 



External Carotid Artery (Fig. 381, 12). 



This artery ought to be considered, because of its volume and direction, as 

 the continuation of the common carotid. It is directed forward, arrives at the 

 posterior border of the great cornu of the os hyoides, passes between it and the 

 stylo-hyoid muscle, and is inflected so as to form an elbow which is turned 

 forward, and afterwards ascends vertically to near the neck of the condyle of 

 the inferior maxilla, at the posterior angle of the hyoid branch. There it 

 bifurcates to give rise to the superficial temporal and internal maxillary arteries. 



In the first part of its course — that is, from its origin to the hyoid bone — the 

 external carotid artery is related : inwardly, to the guttural pouch and the 

 glosso-pharyngeal and superior laryngeal nerves ; outwardly, to the outer belly 

 of the digastric muscle, and the hypoglossal nerve. 



In its second portion, it is comprised between the guttural pouch, the parotid 

 gland, the great cornu of the os hyoides, and the inner side of the posterior 

 border of the inferior maxilla. 



The collateral branches this artery furnishes are three principal — the glosso- 

 facial, maxillo-muscular, and posterior aurinilar. But it also gives oiT others 

 of less importance, which are distributed to the guttural pouch, the guttural 

 glands, and the parotid gland. 



Collateral Branches of the External Carotid. 

 1. Submaxillary, Facial (or Glosso-facial) Artery (Fig. 381, 13). 



This arises from the external carotid, at the point where that vessel passes 

 beneath the stylo-hyoid muscle, and is immediately inflected downwards on the 

 side of the pharynx, between the posterior border of the large cornu of the hyoid 

 bone and the above muscle. It passes in proximity to the anterior extremity of 

 the maxillary gland, crossing Wharton's duct outwardly, and leaves the deep 

 situation it at first occupied, to become more superficial in the submaxillary 

 space, where it rises on the sm-face of the internal pterygoid muscle, and is 

 directed forwards to the maxillary fissure. Turning round this fissure, it climbs 

 on the cheek, in front of the mas?eter muscle, to above the maxillary spine, 

 where it terminates in two small branches. 



