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 of 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- 



. caret, vtiif Suf>. s&y. 

 "Otic vesicle 



Mid., cereb. veiy Coyfl. of sly uses 

 Otic ve$tcl& 

 Isif.ce.reb. veiy 



L.t. veiy o 



. Cere6, 



Otic vesicle Midcereb. vein 



Corjfl.or sir) uses 



Str. sty us 



e veiy ofcereb, 



c . . , , - Sir/t/s * 



5*A '*"? \Itf6et.9i?<,s U 



fyt.ctrd.Kii? \ Su^saj.SLrjus Tr^\y. sinus Sub. cereb. m> 



Lot. fe/^ <y* ^<?arf (/?/. /*. K^ 



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

 head in human embryos. Mall. 



appears, 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 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 

 17 



