ORGANS OF CIRCULATION. 19 1 



the dorsal aorta, or they may leave it as a single trunk, the 

 common iliac. From the internal iliac, arteries arise to supply 

 the various viscera of the pelvis, and also an ischiatic or sciatic 

 artery, which passes out to the dorsal portion of the hind limb, 

 and early forms the chief supply of this appendage. This condi- 

 tion persists in all vertebrates except the mammals. In these 

 the external iliac (after its entrance into the limb known as the 



FIG. 203. Diagram of the chief circulatory vessels in an embryonic sauropsidan. 

 The amnion omitted for clearness. A, allantois; AA, allantoic artery; C, carotid 

 arteries; CA, caudal artery; CV, caudal vein; DA, dorsal aorta; DC, ductus 

 Cuvierii ; H, heart ; HA, hypogastric artery ; L, liver ; OA, omphalomesaraic 

 artery; OV, omphalomesaraic vein ; 57", sinus terminalis ; UV* umbilical (allan- 

 toic) vein; V, vent ; W, vitelline vein. Compare with Fig. 197. 



femoral artery) extends farther into the limb, and usurps the 

 function of the ischiatic, which here supplies only the posterior 

 proximal portion of the appendage. The femoral artery extends 

 down into the bend of the knee, where it is known as the pop- 

 liteal artery, and in the proximal end of the shank divides into 

 an anterior tibial artery which runs along the anterior face of the 

 limb, and a posterior tibial and a peroneal in the calf of the leg. 



