880 THE NERVOUS SYSTEM 



between the external capsule and the putamen, and then through or around the upper part 

 of the putamen into the internal capsule, where they form two groups, the lenticulo-thalamic 

 and the lenticulo-caudate groups. The former terminate in the thalamus and the latter in the cau- 

 date nucleus. On account of its larger size at its origin and its direct linear continuation with the 

 internal carotid, einboli pass more frequently into the middle cerebral artery than into the 

 anterior cerebral artery. One of the lenticulo-caudate arteries which is larger and longer than the 

 others and which is a direct branch from the middle cerebral artery has been called the ' artery 

 of cerebral hemorrhage ' (Charcot), on account of the greater frequency with which it is ruptured. 



(3) The postern-medial central or ganglionic arteries are terminal branches of the posterior 

 cerebral artery. They also enter the anterior perforated substance, but supply the floor of the 

 third ventricle, the posterior part of the thalamus, and the hypothalamic region. 



(4) The postero-lateral group are also terminal branches of the posterior cerebral artery. 

 They supply the posterior part of the internal capsule, the pulvinar of the thalamus, the geni- 

 culate bodies, the corpora quadrigemina and their brachia, the epiphysis, and the cerebral 

 peduncles. 



The cortical group of the cerebral arteries arise from the anastomosing plexus in the pia 

 mater of the cortical surfaces of the hemisphere. They pass into the cortical substance both 

 from the summits of the gyri and from the walls of the sulci. They consist of short, medium, 

 and long branches, and pass at right angles into the gyri. The short branches terminate in the 

 cortical substance; the medium branches supply the more adjacent white substance, and the 

 longer branches pass more deeply into the general medullary centre of the hemisphere. 



All of both the central or ganglionic and the cortical arteries are terminal in the sense that 

 they do not anastomose in the substance of the cerebrum. 



The blood-vascular system of the other divisions of 'the encephalon is in accordance with 

 the same general plan of that of the cerebrum. Slight individual modifications of the general 

 plan are to be expected. 



The blood-vessels of the mesencephalon, in addition to the supply derived from the postero- 

 lateral group of central arteries, include the vessels of the quadrigeminate bodies and those of the 

 cerebral peduncles. The arteries of the quadrigeminate bodies are usually six in number, 

 three for each side the superior, middle, and inferior quadrigeminate arteries. The superior 

 and middle are branches of the posterior cerebral arteries, and the inferior are branches of the 

 superior cerebellar arteries. The superior supply the superior quadrigeminate bodies and the 

 epiphysis; the middle supply both the superior and inferior quadrigeminate bodies, and the 

 inferior the inferior quadrigeminate bodies. They all anastomose on the surface of the stratum 

 zonale, forming a fine-meshed plexus, and from this plexus the terminal branches pass into the 

 substance of the bodies. The veins terminate in the vein of Galen (v. cerebri magna). 



The arteries of the cerebral peduncles form two groups, mesial and lateral. The mesial 

 peduncular arteries are branches of the basilar and the posterior cerebral arteries. They pass 

 to the inner sides of the peduncles and supply the upper and inner part of the tegmentum. The 

 vessels of this group which accompany the fibres of the third nerves are known as the radicular 

 arteries; they supply the root-fibres and the nuclei, which receive no other branches. The lateral 

 peduncular arteries are branches of the posterior cerebral and superior cerebellar arteries. 

 They supply the lateral portions of the peduncles and the outer part of the tegmentum. The 

 veins of the mid-brain terminate in the basilar veins and the vein of Galen. 



The Blood-vessels of the Cerebellum. Six arteries supply the cerebellum; two, the 

 posterior inferior cerebellar, are derived from the vertebral arteries, and the remaining four, 

 two anterior inferior and two superior cerebellar, from the basilar artery. The course and 

 general distribution of the arteries are described in Section V,but here it must be noted that the 

 branches of these six vessels form a rich network in the pia mater on the surfaces of the cerebellar 

 lobes, and that extensions of the plexus pass with the folds of the pia mater into the sulci and 

 fissures. From the superficial plexus terminal branches pass into the interior of the cerebellum 

 and their collaterals form capillary plexuses in the white and grey substance. The extensions 

 of the surface plexus are of three lengths: (1) a longer set, which pass through the cortex of the 

 cerebellum and supply the white substance of the corpus medullare; (2) a set of shorter arterioles 

 which pass through the molecular layer of the cortex and break up in the granular layer; (3) the 

 shortest set pass into the cortex and immediately break up in the molecular layer. The meshes 

 of the capillary plexuses in the grey substance are ovoidal and their axes run radially. The 

 meshes of the plexuses in the white substance are parallel with the nerve-fibres. In addition to 

 the vessels mentioned, a distinct branch is distributed to each dentate nucleus. This springs 

 either from the superior cerebellar or from the anterior inferior cerebellar artery of the corre- 

 sponding side. 



The efferent veins of the cerebellum do not accompany the arteries; they spring from a 

 plexus in the pia mater which receives tributaries from the interior, and they form three groups 

 on each surface, the vermian veins and the lateral veins. The superior vermian vein runs 

 forwards on the upper surface of the vermis and terminates in the vein of Galen. The inferior 

 vermian vein runs backwards and ends in one of the transverse sinuses. The upper lateral 

 veins open into the superior petrosal or transverse sinuses, and the lower lateral veins into 

 the inferior petrosal and transverse sinuses. The vein from the dentate nucleus usually joins the 

 lower lateral veins. 



The Blood-vessels of the Pons. The arteries to the pons are branches of the basilar artery, 

 and of its anterior inferior and superior cerebellar branches. The reticulum in the pia mater 

 is comparatively unimportant, and the branches which enter the substance of the pons form 

 two main groups, the central and the peripheral. The central arteries spring directly from the 

 basilar. They pass backwards along the raphe, giving branches to the adjacent parts, and they 

 terminate in the nuclei in the floor of the fourth ventricle. The peripheral arteries are radicular 

 and intermediate. The radicular branches spring from the peripheral plexus and from the 

 anterior inferior cerebellar arteries; they accompany the roots of the fifth, sixth, seventh, and 



