4 Development of Blood-Vessels of Human Brain 



travasation is complete, filling all the arachnoid spaces and the whole 

 ventricle. After the extravasation was brushed off, the brain substance 

 was still found to be spotted, showing that the extravasation penetrated 

 the brain substance. 



In an embryo of the beginning of the fourth month (80 mm. long) 

 the whole brain was evenly spotted, about one spot to each square milli- 

 meter. Another specimen of the same age and of the same general 

 appearance (No. 234% 80 mm. long) (Fig. 2) was cut into serial sections 

 in order to study the relation of the spots to the surrounding tissues and 

 to the cortical arteries. Around the large cortical arteries (possibly the 

 medullary arteries) there is an extravasation which encircles the vessel 

 as a small spherical body. There is no rupture of the vessel. It indi- 

 cates that at this point the vessel is at least very pervious. There is no 

 extravasation into the ventricle. 



In specimen No. 238 (90 mm. long) both the arteries and the veins 

 were injected without injecting the capillaries. There was no injection 

 of the brain substance, and there is no extravasation of the cortex nor 

 into the ventricles. At the base of the brain and in the falx there is 

 considerable extravasation, apparently coming from the veins. In an 

 embryo of the same age (No. 236, !)2 mm. long) the arterial injection 

 is complete again, with the usual spots of extravasation in the cortex of 

 the cerebral vesicle. The extravasation fills all of the arachnoid spaces as 

 well as the cavities of the ventricle. The injection passes through the 

 medial opening into the fourth ventricle (Majendie), and apparently 

 the ventricles are injected through this opening from the arachnoid. 



It is apparent from the description of the injected embryos that as a 

 rule the extravasation into the arachnoid spaces takes place from the 

 arteries as they penetrate the cortex of the brain, and that in case the 

 veins are injected the extravasation is directly from them. This con- 

 clusion was reached in part by making corresponding injections of em- 

 bryo pigs, many being constantly at my disposal. In general the 

 extravasation is the same in the pig as it is in the human embryos. It 

 frequently appeared, however, as if the India ink injected leaked with 

 even greater ease from the veins and sinuses of the pig"'s brain. In 

 embryos in which the heart had just stopped beating the injected fluid 

 would first fill the jugular veins, then the sinuses, from which the 

 arachnoid spaces filled as readily as did the capillaries. 



When the arachnoid spaces were filled by injecting directly into the 

 lateral ventricles of perfectly fresh embryos, the injected fluid would not 

 pass over into the veins. I made this test repeatedly with live embryos 

 from 3 to 8 cm. long, always with the same result. It is best to inject 



