32 Journal of Comparative Neurology. 



Aside from the three sources of blood enumerated above, 

 the capillaries in the granule layer may receive a supply of 

 blood from certain vessels of class A, some of which may be 

 seen to give branches to the opposite side of the lamina. In other 

 cases the arteriole itself may be seen to cross the medullary 

 layer and distribute itself into capillaries in the granule layer 

 of the opposite side. No example of this appears in the plate. 



From these observations it appears that the vessels in the 

 pia mater on one side of a lamina may be completely occluded, 

 still blood may reach every part of the cortex on that side 

 through certain vessels of class A from the opposite side. 



Directing attention now to the molecular layer, thee 

 sources of blood supply may be recognized. Occasionally arter- 

 ioles of class A may be observed to give off collateral branches 

 while passing through the molecular layer. No instance of this 

 can be shown in the plate. Collateral branches from arterioles 

 B can be observed more frequently. The plate shows good in- 

 stances of this at 2 and 9. But it may be asserted that the 

 molecular layer depends largely upon the capillaries of class C 

 for blood, and as previously stated, there are about fifteen of 

 these to one vessel of class B. Examples of this may be seen 

 at 4 and 7. 



In normal adult domestic cats, so far as my observations 

 extend (and upon this point I have been particularly careful to 

 extend my observations) no peculiarity in the number, size or 

 arrangement of blood vessels marks the layer or region occu- 

 pied by the cells of Purkinje. In other words, the layer of the 

 cells of Purkinje does not constitute a distinct vascular region. 



It may be stated in connection with the subject matter of 

 this paper that the medullary portion is occupied by blood ves- 

 sels arranged in two ways. In the lamina the mesh is elongated, 

 while in the deeper portions the mesh is not elongated. 



Comparing now the layers of the cortex one with another, 

 as regards relative number of capillaries, the arrangement of 

 capillaries, and the relative size of mesh, we may state the fol- 

 lowing propositions. Comparing a like volume of granule layer 

 and molecular layer, the number of capillaries in the granule layer 



