THE DEVELOPMENT OF THE VASCULAR SYSTEM 



253 



si tin urn). From the latter a new vessel grows out to form the straight sinus, 

 and a further growth from the straight sinus forms the large vein of the 

 cerebrum (vein of Galen). The inferior sagittal sinus also represents a new 

 outgrowth at the point of junction of the large vein of the cerebrum and 

 inferior sagittal sinus (Fig. 230, D). During the course of development the 

 lateral vein of the head gradually atrophies and finally disappears, and the 

 inferior petrosal sinus probably represents a new formation which extends 

 from the cavernous sinus to the transverse sinus (Fig. 230, C and D). At 



Ant. cardinal 

 (int. jugular) 



Omphalomesenteric 

 (vitelline) 



Mesonephro; 



Subcardinal 



Iliac 



FIG. 231. Diagram of the venous system of a human embryo of 2.6 mm. 

 Slightly modified from Kollmann's Atlas. 



the point where the inferior petrosal joins the transverse sinus the latter 

 passes out of the skull through the jugular foramen to become the internal 

 jugular vein (anterior cardinal). (Mall.) 



As stated in a preceding paragraph, the anterior cardinal veins extend 

 from the ducts of Cuvier to the head region, passing to the dorsal side of the 

 branchial arches. They are at first paired and symmetrical, but, since the 

 heart is situated in the cervical region, are comparatively short and receive 

 blood from the cervical region through segmental branches which belong only 



