any one white column or group of cells in the grey matter. At the same time it should be noted that within the cord itself (as within the brain), all the arteries are "terminal arteries," in Cohnheim's sense, that is to say, they do not anastomose with other arteries, but each one terminates in its own capillary area, and supplies no other. There is however much variation in the extent of the capillary area supplied by any of the arterial branches, and no definite statement can be made concerning the exact region supplied by any set of arterioles (Kadyi).

The origin and course of the veins of the spinal cord have been described in Vol. II., pp. 533, 534. The most considerable are two longitudinal median vessels, one running along the anterior median fissure along with the anterior spinal artery, and another over the posterior median fissure, unaccompanied by any considerable artery. Both of these median veins have a tortuous course, and the posterior one is frequently broken up into a kind of venous plexus, with longitudinal meshes, which extends over the whole posterior surface of the cord. There is also a less perfect lateral anastomotic chain lying behind the line of exit of the anterior nerve roots. All these vessels communicate freely with one another by lateral offsets. They receive the venous blood from the cord on the one hand, and on the other hand carry it away by veins which accompany, at frequent intervals,, the nerve roots. In the upper part they join the veins of the cerebellum and pons, and the venous sinuses around the foramen magnum. Within the cord their branches anastomose frequently. The vein accompanying the anterior spinal artery receives, like that vessel, very numerous tributaries from the anterior median fissure (central venules): these carry away a large part of the blood from the grey matter; the peripheral venules, which enter the veins of the pia mater which covers the general surface of the cord, chiefly carry away the blood from the capillaries of the white

matter.

Blood-supply of the brain.-The origin and course of the vessels which supply the brain have already been described in the section Angeiology, Vol. II. pp. 411 to 415 (arteries), and 519 to 524 (veins). In passing to their distribution the several arteries, having passed across the subdural space, enter the subarachnoid space and then divide and subdivide into branches, which, in their further ramification on the nervous centres, are supported by the pia mater, and, it may be remarked, are more deeply placed in the various fissures and sulci than the small veins, which do not accompany the arteries, but pursue a different course, and are chiefly seen upon the surface of the pia mater. From the arteries in the pia mater of the hemispheres very numerous small branches pass vertically into the grey matter of the convolutions. Most of these (cortical arteries) at once break up into a close plexus of capillaries for the grey matter; but others (medullary arteries), larger but less numerous, pass through the grey matter, giving off only a few small branches to it, and penetrate for some distance into the medullary centre, where they divide into a long-meshed capillary network. The smaller branches of arteries anastomose together to a certain extent in the pia mater before penetrating into the superficial grey matter (Huebner), but the branches which pass to the chief ganglia, such as the optic thalamus or corpus striatum, do not anastomose with one another.

Moreover, it is to be observed that, whilst the main branches of the arteries are situated at the base of the brain, the principal veins tend towards the upper surface of the hemispheres, where they enter the superior longitudinal sinus, most of them looping forwards as they pass into the sinus, and often entering the dura mater a short distance from the sinus, but more usually having a free course, sometimes of considerable length, through the subarachnoid space in passing from the pia into the dura mater. The veins of Galen, coming from the lateral ventricles and choroid plexuses, run backwards to the straight sinus, in the subarachnoid tissue which lies between the two layers of the velum interpositum.

VOL. III.

It may be convenient here to recapitulate the sources of the blood supply to the several parts of the encephalon.

The medulla oblongata and pons Varolii are supplied by branches from the

Fig. 136. THE ARTERIES OF THE BASE OF THE CEREBRUM. (G. D. T., after Duret, and from nature.) On the left side of the brain the temporal lobe is cut away so as to open the inferior and posterior horus of the lateral ventricle. The mid-brain is divided close above the pons and the posterior cerebral arteries are cut at their origin from the basilar.

Central arteries (to the basal ganglia): am, antero-mesial group arising from the anterior cerebral ; al, antero-lateral group, from the middle cerebral; pm, pl (on the optic thalamus), postero-mesial and postero-lateral groups, from the posterior cerebral.

Choroidal arteries: a ch, anterior, from the internal carotid; p ch (on the splenium), posterior, from the posterior cerebrai.

Peripheral arteries: 1, 1, inferior internal frontal, from the anterior cerebral; 2, inferior external frontal; 3, ascending frontal; 4, ascending parietal, and 5, temporo-parietal, from the middle cerebral ; 6, anterior temporal, 7, posterior temporal, and 8, occipital, from the posterior cerebral.

anterior spinal, the vertebral, the basilar, and the posterior cerebral arteries. The branches enter the pons and medulla oblongata in two sets, lateral or radicular

(following the roots of the nerves), and median,-the latter passing in the raphe to the grey matter on the posterior surface. The valve of Vieussens and the superior peduncle of the cerebellum receive twigs from the superior cerebellar arteries. The choroid plexuses of the fourth ventricle are supplied by the inferior cerebellar arteries.

Cerebellum.-The under surface is supplied by the inferior cerebellar arteries from the vertebral, and the anterior from the basilar. The upper surface is supplied chiefly by the superior cerebellar arteries from the basilar: its posterior portion from the inferior cerebellar.

The crura cerebri derive their blood supply from the posterior communicating and the posterior cerebral arteries. Branches of the latter, and also others from the end of the basilar, enter the posterior perforated space.

The corpora quadrigemina and corpora geniculata are both supplied by the posterior cerebral artery, but branches of the superior cerebellar arteries pass to the inferior corpora quadrigemina.

The optic thalamus is supplied above and on the outer, inner and posterior

Fig. 137.-CORTICAL DISTRIBUTION OF THE MIDDLE CEREBRAL ARTERY. (G. D. T., after Charcot.) Diagrammatic.

CENT., antero-lateral group of central.arteries: 1, inferior external frontal artery; 2, ascending frontal artery; 3, ascending parietal artery; 4, parieto-temporal artery.

sides by branches of the posterior cerebral artery, but its anterior and inner portion receives twigs from the posterior communicating arteries of the circle of Willis and its anterior and outer portion from the middle cerebral.

Cerebral hemispheres.- Frontal lobe. -The superior frontal and anterior twothirds of the middle frontal convolution, with the upper extremity of the ascending frontal, are supplied by the anterior cerebral. The inferior frontal convolution, the posterior extremity of the middle frontal, and the greater part of the ascending frontal convolutions are supplied by the middle cerebral. The orbital surface is supplied, outside the orbital sulcus, by the middle cerebral: within that sulcus (including the olfactory bulb) by the anterior cerebral.

Parietal lobe.-All the convolutions of the parietal lobe are usually supplied by the middle cerebral artery.

Occipital lobe. This lobe is supplied entirely by the posterior cerebral artery. Temporal lobe. The superior and upper parts of the middle temporal convo

Fig. 138.-DIAGRAMS SHOWING THE AREAS OF CORTICAL DISTRIBUTION OF THE ANTERIOR, MIDDLE, AND POSTERIOR CEREBRAL ARTERIES RESPECTIVELY. (E. A. S.)

The area supplied by the middle cerebral frequently extends to the upper border of the hemisphere in the region of the parietal lobe, and therefore somewhat further than is represented in A.

lutions are supplied by the middle cerebral artery. The lower portion of the lobe by the posterior cerebral.

Inner surface of the hemispheres.-The whole anterior and upper portion, as far back as the parieto-occipital fissure, is supplied by the anterior cerebral artery; the cuneate lobule and the occipito-temporal region by the posterior cerebral.

The distribution of arteries to the several parts of the cerebral cortex is illustrated in the accompanying diagrams (fig. 138).

The corpus callosum is chiefly supplied by the anterior cerebral.

The grey substance at the base of the cerebrum is supplied by small twigs from the adjacent vessels of the circle of Willis, or from the roots of the cerebral vessels which pass off from the anastomosis.

Central parts-corpus striatum.-Both nucleus caudatus and nucleus lenticularis

are supplied almost exclusively by the middle cerebral artery, the numerous branches to these parts entering through the foramina in the anterior perforated space (fig. 136). They are divided by Duret into lenticular, lenticulo-striate, and lenticulooptic (lenticulo-thalamic). These pass directly to their destination without anastomosing with one another, and traverse the zones of the lenticular nucleus and the internal capsule, to terminate finally in the caudate nucleus and optic thalamus (fig. 139). One in particular of the lenticulo-striate arteries which passes through the outer part of the putamen is very frequently the seat of hæmorrhage, and it has accordingly been termed by Charcot the "artery of cerebral hemorrhage " (fig. 139, x).

The anterior part of the caudate nucleus is also supplied by the anterior cerebral,