114 



LECTURE IV. 



this manner filled the place of the vasa serosa (which the 

 older writers imagined as a complement to the capilla- 

 ries for these ultimate purposes of nutrition) with some- 

 thing definite, by means of which the circulation of nu- 

 tritive juices is rendered possible in parts which are in 

 themselves poor in vessels. To keep to bone, we should 



FIG. 35. 



scarcely be justified in assuming the existence of vasa 

 serosa in it. The hard basis-substance is throughout 



Fig. 35. Section of an osseous plate from the arachnoid of the cerebrum, but 

 quite normal in its structure. A branching vascular (medullary) canal is seen with 

 canaliculi opening into it, and leading to the bone corpuscles. 350 diameters. 



