172 



GEORGE L, STREETER 



TABLE 1 



Superior sagittal sinus 



Injected specimens. 



SUMMARY 



If now we look back and bring together the essential features 

 in the development of the venous sinuses of the dura mater, we 

 will find their development may be analyzed somewhat as follows : 

 (1) There is first the establishment of the primary arrangement 

 for the drainage of the head; (2) this is followed by a separation 

 of the veins of the head into two and finally three separate layers 

 or strata, of which the middle layer constitutes the dural veins; 

 (3) certain adjustments of the dural channels are made neces- 

 sary by the environmental changes in the region of the middle 

 and internal ear; (4) similar and still greater adjustments of the 

 dural channels follow the marked growth and change in form of 

 the brain; (5) and finally, there are the late histological changes 

 in the vein walls that convert them into the adult sinuses. This 

 last or histological feature is not taken up in the present paper. 

 The other four features, however, will now be outlined. 



