72 THE VASCULAR SYSTEM. 
front of the crus cerebri, and passing above the third nerve, joins the posterior cerebral 
artery forming part of the circle of Willis. It gives branches to the optic tract, the crus 
cerebri, the interpeduncular region, and the uncinate convolution of the brain. The 
posterior communicating artery varies much in size; it may be small on one or both 
sides, sometimes it is very large on one side; occasionally it replaces the posterior 
cerebral artery, and it sometimes arises from the middle cerebral artery. 
(7) The anterior chorioidal (a. chorioidea) is a small branch, which also rises near the 
termination of the internal carotid ; it passes backwards and outwards, between the crus 
cerebri and the uncinate convolution, to the lower and front part of the chorioidal fissure 
which it enters, and it terminates in the chorioidal plexus in the descending cornu of the 
lateral ventricle. It supplies the optic tract, the crus cerebri, the uncinate convolution, 
and the posterior part of the internal capsule. 
(8) Anterior Cerebral Artery (a. cerebri anterior). This is the smaller 
of the two terminal branches of the internal carotid. It passes forwards and in- 
wards, above the optic chiasma and immediately in front of the lamina cinerea, to 
the commencement of the great longitudinal fissure, where it turns round the genu 
of the corpus callosum, and runs backwards to the parietal lobe of the brain. At 
the commencement of the ereat longitudinal fissure it is closely connected with its 
fellow of the opposite side by a wide but short anterior communicating artery (a. 
communicans anterior), and in the remainder of its course it 1s closely accompanied 
by its fellow artery of the opposite side. 
Branches.— Branches of all the cerebral arteries are distributed both to the basal 
ganglionic masses of the brain and to the cerebral cortex ; they therefore form two dis- 
tinct groups—(a) central or ganglionic ; (/) cortical. 
The branches of the anterior cerebral include : 
(a) Central or ganglionic branches. —The antero-mesial arteries, a small group of 
vessels, constitute the central branches of the anterior cerebral artery ; they pass upwards 
into the base of the brain in front of the optic chiasma, and supply the rostrum of 
the corpus callosum, the lamina cinerea, and the septum lucidum. 
(b) Cortical branches. — (b') Internal orbital, one or more small branches which 
supply the internal orbital convolution, the gyrus rectus, and the olfactory lobe. 
(4°) Anterior internal frontal, one or more branches which are distributed to the 
anterior and lower part of the marginal convolution, and to the anterior portions of the 
superior and middle frontal convolutions. 
(6°) A middle internal frontal is distributed to the posterior part of the marginal 
convolution, and to the upper portions of the superior and ascending frontal and ascend- 
ing parietal convolutions. ; 
(0+) The posterior internal frontal runs backwards to the quadrate lobule. It sup- 
plies the corpus callosum, the quadrate lobe, and the upper part of the superior parietal 
lobule. 
(9) Middle Cerebral Artery (a. cerebri media)—The middle cerebral is the 
larger of the two terminal branches, and the more direct continuation of the 
internal carotid artery. It passes outwards in the fissure of Sylvius to the outer 
surface of the island of Reil, which it crosses; and divides, in the posterior 
limiting sulcus of Reil, into parieto-temporal and temporal terminal branches. 
Branches.—(a) Central or ganglionic.—Numerous and very variable in size. These 
branches are given off at the base of the brain, in the region of the anterior perforated 
space. Two sets, known as the internal and the external striate arteries, are distinguishable. 
(a') The internal striate arteries pass upwards through the two inner segments of 
the lenticular nucleus (globus pallidus) and the internal capsule to terminate in the 
caudate nucleus. They supply the anterior portions of the lenticular and caudate nuclei 
and of the internal capsule. 
(a*) The external striate arteries pass upwards through the outer segment (puta- 
men) of the lenticular nucleus, or between it and the external capsule, and they form two 
sets, an anterior, the lenticulo- -striate, and a posterior, the lenticulo-optie ; both sets tra- 
verse the lenticular nucleus and the internal capsule, but the lenticulo-striate arteries 
terminate in the caudate nucleus, and the denticu/o-optic in the optic thalamus. One of 
the lenticulo-striate arteries, which passes in the first instance round the outer side of the 
lenticular nucleus, and afterwards through its substance, is larger than its companions ; it 
frequently ruptures, and is known as the artery of cerebral hemorrhage. 
