CAROTID ARTERY. 



493 



backwards and outwards, enters the tractus 

 opticus, supplies the pia mater of the middle 

 lobe of the brain and the optic thalamus, and, 

 entering the inferior cornu of the lateral ven- 

 tricle, spreads out its branches in the choroid 

 plexus. 



After having given off the choroid artery, the 

 internal carotid divides always at an obtuse 

 angle, and at the internal extremity of the fis- 

 sure of Sylvius, into two branches, the an- 

 terior and the middle cerebral, of which the 

 latter is much the larger vessel : sometimes 

 the lateral communicating artery arises at the 

 place of this division, and forms with these 

 branches a sort of tripod. 



T/ie anterior cerebri, also called the artery 

 of the corpus callosum, is always smaller than 

 the media cerebri; it passes upwards, forwards, 

 and inwards to the fissure which separates the 

 anterior lobes of the cerebrum, passing over 

 the optic nerves, and inferior to the internal 

 origin of the olfactory: on entering the above- 

 mentioned fissure, it approaches closely to the 

 corresponding branch of the opposite side, 

 with which it communicates by a large and 

 very short transverse branch, called the anterior 

 communicating artery, by which the circle of 

 Willis is completed anteriorly : sometimes 

 this branch is double, and occasionally we find 

 it partially double, in consequence of a forking 

 of one of its extremities ; its place is sometimes 

 supplied by a fasciculus of small branches ; it 

 gives off", especially when it is unusually long, 

 a number of small twigs, which pass upwards 

 and backwards to the septum lucidum, fornix, 

 and corpus callosum. 



From the place of this communication the 

 trunk of the anterior cerebri passes forwards 

 under the corpus callosum, giving off consi- 

 derable branches to the inferior and internal 

 part of the anterior lobe of the cerebrum ; it 

 then turns round to the anterior extremity of 

 the corpus callosum, mounts up on the internal 

 surface of the hemisphere of the cerebrum, 

 and divides into many branches, the anterior 

 and superior of which supply the convolutions 

 on their internal surface, while the posterior 

 take a lower course along the upper sur- 

 face of the corpus callosum, at the posterior 

 extremity of which they take an ascending 

 direction. All these branches extend to the 

 superior surface of the cerebrum, and anasto- 

 mose with those of the media cerebri and the 

 posterior cerebri, which is furnished by the ver- 

 tebral. 



Besides these large branches into which the 

 arteria callosa divides superiorly, it gives off 

 from its inferior and concave side, a vast number 

 of smaller branches, which penetrate the corpus 

 callosum. 



Sometimes, instead of being connected by 

 the communicating branch, the anterior cerebral 

 arteries of opposite sides unite, forming a single 

 trunk, which runs forward for some little dis- 

 tance, and then divides into a right and left 

 branch ; this junction is the more remarkable, 

 on account of its analogy to the union of the 

 two vertebral arteres in forming the single 

 trunk of the basilar on the median line. 



The media cerebri, from its greater size com- 

 pared with the anterior branch, appears, as it 

 were, the continuation of the trunk of the 

 carotid ; it passes outwards and backwards, in 

 the fissure of Sylvius, and divides into two 

 branches, the subdivisions of both of which 

 are distributed over the pia mater of the anterior 

 and middle lobes of the brain, anastomosing 

 in front with the anterior cerebri, and behind 

 with the posterior cerebri from the basilar : 

 this artery at first gives branches at the base of 

 the brain to the pia mater on the crus cerebri ; 

 one of these, larger than the others, enters the 

 inferior cornu of the lateral ventricle, where it 

 is lost in the choroid plexus. 



The anterior and middle cerebral arteries are 

 not always similarly disposed on opposite 

 sides ; it not ^infrequently happens, as Haller 

 has remarked, that the two large trunks of the 

 middle cerebral arteries are given off by the 

 right carotid, and the two anterior from the 

 left carotid, while the three others come from 

 the right : considering these anomalies with 

 that of the union of the two cerebral already 

 mentioned, we here find a very remarkable 

 repetition of many of the varieties exhibited by 

 the mode in which the trunks that spring from 

 the arch of the aorta take their origin. 



For the BIBLIOGRAPHY, see that of ANATOMY 

 (INTRODUCTION), and of ARTERY. 



(J. Hart.) 



The following observations are to be regarded 

 as supplemental to the preceding article. 



There is no fact more worthy of the atten- 

 tion of the practical surgeon, as regards the 

 anatomical history of the carotid artery, than 

 the free anastomosis which exists between the 

 external and internal carotids of both sides at 

 nearly all the stages of their course. This is 

 especially the case with the external carotid 

 arteries which anastomose at numerous short 

 intervals from their origin to their termination, 

 where they likewise communicate with some 

 small ramifications of the internal carotids. 

 Nor is the communication between the internal 

 carotids less free, although it is less frequent : 

 this communication is formed within the cra- 

 nium at the anterior segment of the circle of 

 Willis. Moreover, by means of the posterior 

 communicating artery the internal carotid anas- 

 tomoses with the posterior cerebral, and there- 

 by with the subclavian, through the medium of 

 the vertebral artery. And farther, by the anas- 

 tomoses of the superior thyroid artery with the 

 inferior, and of the occipital with the cervicalis 

 ascendens, profunda, and vertebral, a commu- 

 nication is established between the external 

 carotid artery and the subclavian. 



From the knowledge of the communication 

 thus existing between these several portions of 

 the arterial system of the neck and head, we 

 may deduce some very useful inferences. 



1. It is evident that the carotids of both 

 sides may be injected by even a coarse injec- 

 tion, from a pipe introduced into the artery of 

 one side. This is a fact well known to every 

 practical anatomist. 



