MEMBRANES AND BLOOD VESSELS 447 



The postero-median central arteries arise close to the origin of the parent 

 trunk. Thy proceed upwards, in the interval between the pedunculi cerebri, 

 and, piercing the substantia perforata posterior (O.T. posterior perforated 

 space), they supply the thalami and the medial parts of the pedunculi 

 cerebri. 



The postero -lateral central arteries are a group of small slender twigs 

 which arise on the lateral surface of the pedunculus cerebri, and go to the 

 corpora quadrigemina and the thalamus. 



The posterior chorioidal artery, somewhat larger, goes to the tela 

 chorioidea of the third ventricle and the chorioid plexus of the lateral 

 ventricle (Figs. 178 and 179). 



The temporal branches, two or three in number, turn laterally, over the 

 hippocampal gyrus, and ramify on the under surface of the temporal lobe 

 of the cerebrum (Figs. 178 and 180). 



The calcarine branch follows the calcarine fissure to the occipital pole 

 of the cerebral hemisphere, round which it turns to reach the lateral surface 

 of the occipital lobe. It is the chief artery of supply to the cuneus and the 

 lingual gyrus, and is therefore specially concerned in the nutrition of the 

 visual centres of the cerebral cortex (Fig. 1/8). 



The parieto-occipital artery is the smaller of the two terminal branches 

 of the posterior cerebral. It runs upwards in the parieto-occipital fissure, 

 and reaching the upper margin of the cerebrum it turns round it to 

 reach the lateral surface of the occipital lobe. It supplies branches to the 

 cuneus and proecuneus (Figs. 178, 180). 



Arteria Carotis Interna. The cut extremity of this great 

 vessel lies on the lateral side of the optic chiasma, in the 

 angle between the optic nerve and the optic tract. At the 

 substantia perforata anterior, close to the commencement of 

 the lateral fissure, it ends by dividing into the anterior and 

 middle cerebral arteries (Fig. 1 79). The middle cerebral artery 

 is the larger of the two terminal branches, and, as it enters the 

 lateral (O.T. Sylvian) fissure, it appears to be the continuation 

 of the parent trunk. The anterior cerebral artery, on the 

 other hand, proceeds medially from the internal carotid at 

 almost a right angle. This explains how it is that emboli 

 pass more frequently into the middle cerebral than into the 

 anterior cerebral artery. From the internal carotid artery, 

 after it has emerged from the cavernous sinus (p. 331), the 

 following branches arise : 



1. Ophthalmic (already studied, 



P- 34i)- 



2. Posterior communicating. 



3. Chorioidal. 



4. Middle cerebral. 



5. Anterior cerebral. 



Arteria Communicans Posterior. This, as a rule, is a 

 slender branch which passes posteriorly to join the posterior 

 cerebral between its postero-median and postero-lateral groups 

 of basal twigs (Fig. 181). 



Arteria Chorioidea. The chorioidal artery enters the 



