VENOUS SINUSES OF THE DURA MATER 



161 



-LEXUS ANT 



PLEXUS 

 SAGITTALIS 



SIN TRANSVERSUS 



V OPTHAL 



SIN. CAVERNOSUS 



Fig. 5 Profile reconstruction of the dural veins in a human embryo 24 mm. 

 long (No. 632, Carnegie Collection). The point marked 'x' is the junction of the 

 sigmoid portion of the transverse sinus with the internal jugular vein. Enlarged 

 about 4 diameters. 



of the anterior dural plexus at this time (compare figs. 4 and 5 

 with figure 3). In the first place, the anterior dural plexus an- 

 nexes itself to the middle dural plexus and drains backward 

 through this into the newly established channel dorsal to the 

 otic capsule. We will therefore, from now on, refer to the com- 

 bined anterior and middle dural plexuses as the anterior dural 

 plexus, on the basis that the middle plexus has now lost its iden- 

 tity. In the second place, there is differentiated along the mar- 

 gin of the cerebrum and between the hemispheres, a subdivision 

 of the anterior dural plexus that is eventually to constitute the 

 superior sagittal sinus (marked 'plexus sagittalis' in figs. 4-5). 

 Examination of photographs and sketches of embryos of about 

 this age shows that there is a tendency to the formation of a 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 18, NO. 2 



