DEVELOPMENT OF THE VEINS 



275 



vein. The corresponding portion of the new left vein with the transverse anas- 

 tMnosis becomes the left common iliac vein. The blood from these veins is now 

 drained by the unpaired inferior vena cava which is composed of the following 

 veins: (1) the common hepatic and right hepatic veins (primitive right vitelline) ; 

 (2) the vein of the plica venae cavse; (3) an inter-renal portion of the right subcar- 

 dinal vein with its great mesial anastomosis; (4) the new vein which replaces the 

 right posterior cardinal. 



The permanent kidneys take up their positions opposite the great anastomosis 

 between the subcardinals and at this point the renal veins are developed (Fig. 



Aiiditory vesicle 



Vena capitis medialis 

 Trigeminal nerve 

 Ophthalmic vein 



Superior sagit- 

 tal sinus 



Confluence a} the sinuses 



Primilive jugular sagittal 

 vein ?7'«.7/c 



Middle cerebral vein 



Posterior cerebral 

 vein 



Anterior cerebral vein \ 

 Ophthalmic vein 

 Trigeminal nerve 



Vena capitis 

 lateralis 



Auditory vesicle 



Confluence of the 



sinuses 

 Superior 



Anterior cerebral vein 

 Middle cerebral vein 

 Auditory vesicle 



D 



Inferior sagittal sinus Straight sinus 



Confluence 

 of the sinuses 



Trigeminal nerve 

 Ophthalmic vein 



Posterior 



cerebral 



vein 



Jugular 

 vein 



Great cerebral vein 

 Superior sagittal 

 sinus 



Superior 

 petrosal 

 sinus 

 Trans- 

 verse 

 sinus 



Auditory vesicle 

 : vein | Inf. petrosal sinus 

 Trigeminal nerve 



Fig. 284. — ^Four diagrams showing the development of the veins of the head (after Mall). A, At four 

 weeks; B, at five weeks; C, at the beginning of the third month; D, from an older fetus. 



Vena capitis 

 lateralis 



Anterior cere- 

 bral vein 

 Sphenopari 

 etal sinus 



282 B) ; the longer left renal vein differs from the right in that proximally it rep- 

 resents a left portion of the anastomosis itself (Fig. 282 D). A cephahc portion 

 of the left subcardinal vein persists as the left suprarenal vein, which thus opens 

 into the left renal instead of Joining the inferior vena cava as does the right 

 suprarenal vein of similar origin. The left spermatic or ovarian vein early drains 

 into the4eft caudal border of the great subcardinal anastomosis, which as we have 

 seen contributes to the left renal vein. The right spermatic or ovarian vein opens 

 into the right border of that portion of the subcardinal anastomosis which is in- 



