THE COMMON CAROTID AETEEIES. 581 



POSTERIOR COMMUNICATING ARTERY. This vessel is inflected backward on 

 the side of the pituitary gland, and anastomoses behind it with the 

 posterior cerebral artery. 



MIDDLE CEREBRAL ARTERY. This vessel separates itself from the an- 

 terior cerebral artery, external to the chiasma of the optic nerves, is lodged 

 in the fissure of Sylvius, passing through it in a flexuous manner, and at its 

 extremity separates into several branches which ramify on the lateral and 

 superior faces of the brain, and anastomose by their terminal divisions with 

 the posterior and anterior cerebral arteries. 



ANTERIOR CEREBRAL ABTERY. This enters immediately above the com- 

 missure of the optic nerves, and proceeds inwards to unite, in the middle 

 line, with the opposite artery, forming with it a single vessel. This median 

 artery (or arteria corporis callosi) enters the longitudinal fissure of the brain 

 by bending round the anterior extremity of the corpus callosum, and, after 

 a short course, divides into two branches which pass from before to behind, 

 one to the right, the other to the 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 ophthalmic. 



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

 receive the nieningeul branch of the ophthalmic, the calibre of which often 

 even surpasses that of these vessels. 



EXTERNAL CAROTID ARTERY. (Fig. 286, 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 branch of the os hyoides, passes between 

 it and the great 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 responds : 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 branch 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 auricular. But it also gives off 

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

 guttural glands, and the parotid gland. 



1. External Maxillary, Facial, or Glosso-facial Artery. (Fig. 286, 13.) 



It originates from the external carotid, at the point where that vessel 

 passes beneath the great hyoid muscle, and is immediately inflected downwards 

 on the side of the pharynx, between the posterior border of the large branch 

 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, 

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