158 GEORGE L. STREETER 



was confined to the veins that are under discussion. For the 

 sake of comparison, another embryo shghtly older (No. 632, 24 

 mm. Carnegie Collection) was studied and a profile reconstruction 

 of it is shown in figure 5. 



On examination of figure 4 it will be seen that the primary 

 head vein is now separated into its adult parts. In the trigem- 

 inal nerve region we can speak of it as the cavernous sinus, re- 

 ceiving as tributaries the ophthalmic veins and a large cerebral 

 vein draining the lateral wall of the diencephalon. This vein 

 belongs to the cerebral vein-system and runs for the most of its 

 course through the pia-arachnoid membranes. It penetrates the 

 dura and runs a short dural course before joining the cavernous 

 sinus. It may be regarded as one of the diminishing number of 

 channels that drain the cerebral venous system into the dural 

 system. Besides these there are smaller tributaries from a net- 

 work in the region of the semilunar ganglion. No tributaries 

 were detected flowing into the cavernous sinus from the cerebral 

 hemisphere, such as were found up to this time; all this blood now 

 flows in the opposite direction, caudalward into the developing 

 transverse sinus. 



Tracing the cavernous sinus backward, it can be seen that the 

 interruption between it and the internal jugular vein is complete, 

 though there is still a remnant of that connection, which extends 

 as a blind channel a short way along the facial nerve. It is 

 interesting to note that we occasionally find in the adult skull 

 a persistent foramen, the 'foramen jugulare spurium' of Luschka, 

 which corresponds to the exit of this decadent channel. The vein 

 itself, however, has never been described as persisting, although 

 it exists normally in lower forms as a drainage for the anterior 

 part of the brain, passing through this extracranial course to 

 empty into the internal jugular vein. In the stage we -are study- 

 ing the drainage of the cavernous sinus is upward over the semi- 

 lunar ganglion into what may now be recognized as the transverse 

 sinus. This communication is through a short channel that ap- 

 proximately represents the original trunk of the middle dural 

 plexus, and constitutes the superior petrosal sinus. This channel 

 is designated by Markowski ('11) as the 'vena prootica,' and he 



