576 VESSELS OF BRAIN AXD COED. 



On a careful examination of the connections of these bodies it will he 

 found that the elevations found on the outer surface of the dura mater 

 and within the longitudinal sinus, in no instance take origin in those 

 positions, but that they are grape-like bodies which are attached more 

 deeply, and in their growth have perforated the dura mater. Their pre- 

 cise origin and nature were long the subject of conflicting opinions, but 

 it has been satisfactorily shown by Luschka that they are only an en- 

 larged condition of normal villi of the arachnoid, and that no other 

 structure is involved in their formation. On each side of the sinus, and 

 communicating with it, are large venous spaces in the dura mater ; into 

 these the villi project even in new-born animals, and those which per- 

 forate the dura mater and appear on the surface have their inner parts 

 in such spaces. Each villus is covered by an epitheliated membrane, 

 continuous with the arachnoid. Outside this is another fine membranous 

 sheath, proceeding from the dura mater, and the interval between the 

 two is continuous with the subdural space. Within the villus is a 

 spongy trabecular tissue, continuous with the subarachnoid tissue, and 

 of similar structure. (Luschka, in Midler's Archiv. 1852; and "Die 

 Adergeflechte des Menschlichen Gehirns," 1855. See also Cleland " On 

 Tumours of the Dura Mater, &c." in the Glasgow Medical Journal, 

 1863. Axel Key and Eetzius, Nordiskt Med. Arkiv. 1870 — 1874, and 

 Yirchow's Jahresbericht.) 



BLOOD-VESSELS OF THE BRAIN ANT> SPINAL COED. 



The origin and course of these vessels have already been described 

 in the Section Angeiology. In passing to their distribution the several 

 arteries, having passed across the arachnoid cavity, enter the sub- 

 arachnoid space and then divide and subdivide into branches, which, in 

 their farther ramification in the nervous centres, are supported by the 

 pia mater, and, it may be remarked, ore 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 seen upon the surface 

 ot the pia mater. 



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 h emispheres, where they enter the 

 superior and inferior longitudinal sinuses : the veins of Galen, how- 

 ever, coming from the lateral ventricles and choroid plexuses, run back- 

 wards to the straight sinus. 



BLOOD SUPPLY OF THE BEAIN. 



It may be convenient here to recapitulate the sources of the blood-supply to 

 the several parts of the encephalon. 



The medulla oblong-ata and Pons Varolii are supplied by branches from 

 the anterior spinals, the vertebrals, the basilar and the posterior cerebrals. The 

 branches enter the pons and medulla in two sets, lateral or radicular, and median, 

 — the latter passing in the septum to the grey matter on the ujjper surface. 



Cerebellum.. — The under surface is supplied by the posterior inferior cere- 

 bellar arteries from the vertebrals. and the anterior inferior from the basilar. 

 The iqjpcr surface is supplied chiefly by the superior cerebellar arteries from the 

 basilar : its posterior portion from the posterior inferior cerebellar. 



Cerebrum. — Conxolnt'wns, outer surf are, frontal lobe. — The superior frontal 

 and anterior two-thirds of the middle frontal convolution, with the upper ex- 

 tremity of the ascending frontal, are supplied by the anterior cerebral. The 



