430 EDWARD HORNE CRAIGIE 



following Ekker (including Luschka, Henle, Frey) reproduced 

 his account, but added nothing (according to Duret). Gerlach 

 soon afterward made some similar observations, but without 

 extending the knowledge of the subject. 



The vessels on the surface of the brain and the main branches 

 which enter its substance were well described in the eighteenth 

 century by Haller, Willis, Vicq d'Azyr, and others, and their 

 observations were extended and made more exact by many 

 later workers. 



Heubner (72, 74) was "the first to investigate methodically 

 the distribution of the different branches of the cerebral arteries" 

 (Beevor). He divided the arterial supply of the hemispheres 

 into basal and cortical, the vessels of the former group being 

 all 'end arteries,' without anastomotic intercommunications, 

 while those of the latter group anastomose freely in the pia mater. 

 Cohnheim (72) concluded that there were a few anastomoses 

 between the arteries near the circle of Willis, but that the arteries 

 to the brain were practically 'end arteries' in the strict sense, 

 and that anastomoses within the brain substance were insignifi- 

 cant when present at all. 



About the same time, Duret (73, 74) published an extensive 

 study of the vascular supply of the brain. He found the cells 

 of the bulbar nuclei to be surrounded by a very fine capillary net, 

 while the mesh in the white tracts was large. In the cerebral 

 cortex the outer 0.1 mm. contains large quadrangular meshes 

 parallel to the surface, forming fine anastomoses between the 

 arteries which penetrate the convolutions. The next 2 mm. 

 is filled with rather fine polygonal capillary meshes, formed chiefly 

 by collateral and terminal branches of the cortical arteries. The 

 inner 1 mm. has a transitional network, with larger meshes, but 

 much less elongate than those of the white matter, into which 

 they pass. In the white matter the length of the meshes is three 

 or four times the diameter of those in the gray matter, and they 

 run parallel to the principal bundles, which they seem to surround. 

 Throughout the central nervous system the cellular regions are 

 more highly vascular than the rest. Duret remarks upon the 

 fact that there is a complete correspondence in the vasculari- 



