THE ANATOMY OF A SIX MM. PIG EMBRYO 



101 



pair of aortic arches, the descending aortae are continued forward into 

 the maxillary processes as the internal carotids. Caudal to the aortic 

 arches, the descending aortae converge, unite opposite the cardiac end of the 

 stomach, and form the median dorsal aorta. From this vessel and from the 

 descending aortae paired, dorsal inter segmental arteries arise. From the 

 seventh pair of these arteries (the first pair to arise from the medial dorsal 

 aorta) there are developed a pair of lateral branches to the upper limb buds. 



Spinal cord 

 Ant. cardinal vein 



Cervical sinus 



Pericardial cavity 



A trial junction of sinus venosus 

 Sinus venosus 



Right vitelline vein 



Liver 

 Large venous sinusoid of liver 



Hepatic diverticulum (cut) 

 Yolk stalk 



Portal vein 



Cephalic limb 



intestinal loop 



Right umbilical vein 



Vitelline artery 



Caudal limb. 



intestinal loop 



Right umbilical arter 



Dorsal aorta' 



Notochord 

 Ant. cardinal 

 vein 



Pharynx 



Pericardial 



cattily 



Left common 



cardinal vein 



Left horn of sinus venosus 



Left vitelline vein 

 Dtiftus venosus 

 Ant. limb bud 

 Inf. vena cava 

 Dorsal pancreas 

 Left vitelline vein 

 Common vitelline vein 



Left umbilical vein 



'Sup. mesenteric vein 

 Left umbilical artery 

 Post, limb bud 

 'Spinal cord 



FIG. 102. Reconstruction in ventral view of a 6 mm. pig embryo, to show the vitelline and 

 umbilical veins, the latter opened (original drawing by K. L. Vehe). X 22. In the small 

 orientation figure (cf. Fig. 105) the various planes are indicated by broken lines * *. 



These vessels are the subclavian arteries. From the dorsal aorta there are 

 also given off ventro-lateral arteries to the glomeruli of the mesonephros, 

 and median ventral arteries. Of the latter, the cceliac artery arises opposite 

 the origin of the hepatic diverticulum. The vitelline artery takes origin by 

 two or three trunks caudal to the dorsal pancreas. Of these trunks, the 

 posterior is the larger and persists as the superior mesenteric artery. 

 Thyng has figured three trunks of origin in the 7.8 mm. pig. These unite 

 and the single vitelline artery branches in the wall of the yolk sac. 



Opposite the lower limb buds the dorsal aorta is divided for a short 



