THE DEVELOPMENT OF THE VASCULAR SYSTEM. 



255 



represents the inferior cerebral vein itself (Fig. 230, compare C and D). 

 The caudal end of the superior sagittal sinus becomes dilated to form the con- 

 fluence o" the sinuses (confluens sinuum) . 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 dis- 



Ant. card, vet? Sufi, say.^tyus 

 vesicle 



Lit. veil? of 



Mid., cereb. vein Co?fl. of siyuses 



lyf. cereA. vei 



Lit. vein of fyea.d Ca.v, sinus Su^dereb. veir? 



Coy ft. of 5 iff uses 



La rye rein of cere b. 

 5tr. Sinus \ Inf. saa. sin us 



t/i 



Sub. cereb, vein 



5ub. 5&ff. Sini/s 

 Lat. veiy of fyead 



tf. cereb. 



Cav. sit] us 

 lyf. pet. siqus 



sinus 5ub. cereb. Vein 

 ' 



IIG. 230. Diagrams representing four stages in the development of the veins of the 

 head in human embrvos. Mall. 



appears, and the inferior petro sal sinus probably represents a new formation which 

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

 At 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). 



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 





