2 Development of Blood- Vessels of Human Brain 



fluid is taken up by the heart and is pumped through the arterial system. 

 When all the arteries are full the beat of the heart may be arrested by 

 cooling the embryo. A second injection into the liver vtdth a different 

 fluid (and for this purpose I usually employed aqueous Prussian blue) 

 fllls the entire venous system. More frequently single injections were 

 made of the arteries or of the veins by injecting India ink into the liver 

 either before or after the heart had ceased to beat. India ink, being 

 resistant, is preferred, for embryos injected with it can be hardened in 

 alcohol and cleared in a one per cent solution of caustic potash and 

 preserved in glycerine. Such specimens are perfectly transparent, show- 

 ing the arrangement of the vessels beautifully and their relation to the 

 structures within the head. Sagittal sections of whole embryos are also 

 very valuable for study, for the half brain is easily peeled out, leaving 

 the injected membranes intact within the head. 



It is difficult to make complete injections of the veins of the head in 

 dead embryos without extravasations into the araclinoid spaces. So 

 frequent is this extravasation that one is inclined to think that the vessels 

 of the brain, especially the veins, have open communication with these 

 spaces. But since the arachnoid spaces are always free from blood, and 

 since complete injections with India ink made by the contraction of the 

 heart in live embryos do not form extravasations, it must be concluded 

 that the vessels are closed in life. A similar communication has been 

 demonstrated by Key and Eetzius ' in the adult brain by injecting Prus- 

 sian blue into the arachnoid spaces. Frequently the fluid passes over 

 into the sinuses through the Pacchionian bodies, showing that here again 

 the communication is easily established. This question will be taken up 

 again in the description of the specimens. 



I shall first describe the blood-vessels of the brains of eight embryos 

 of the third month, which had been injected, then take them up in 

 regular order, beginning with a reconstructed specimen of the fourth 

 week. At this point I wish to express my great obligations to Mr. Brodel 

 for much of this valuable material. He has an exceptional opportunity 

 to obtain many fresh specimens which can be injected, and I sincerely 

 hope that physicians will continue to send him all the embryos they 

 obtain, for Mr. Brodel makes the greatest possible use of them. 



Injections. 



Unfortunatley there is a tendency for the Prussian blue which has 

 been injected to extravasate over the surface of the brain, interfering 



'^Key and Retzius: Studien in der Anatomie des Nervensystems und des 

 Bindegewebes. Stockholm, 1875, p. 218. 



