104 



THE STUDY OF SIX AND TEN MILLIMETER PIG EMBRYOS 



The umbilical veins, taking their origin in the walls of the chorion and 

 allantoic vesicle, lie caudal and lateral to the allantoic stalk and anasto- 

 mose (Figs. 102 and 105). Before the allantoic stalk enters the body, 

 the umbilical veins separate and run lateral to the umbilical arteries. 

 The left vein is much the larger. Both, after receiving branches from the 



Aortic arch i Seessel's pouch 

 Aortic arch 2 \ ^Jg^>>^ ^- Isthmus 

 Pharynx 

 Thyreoid 



Aortic arch 



106 



Notochord 



Aortic arch 4 

 107 



Aortic arch 6 and_ 

 pulmonary artery 



108 

 Esophagus 



109 

 Trachea 



no 



R. lung 

 in 



Caliac artery 



114 

 Ventral pancreas 



Dorsal pancreas 

 Gall bladder 



L. umbilical vein 



Vitelline artery 



Int. carotid artery 

 106 



Rathke's pouch 

 Optic recess 



Telencephalon 

 Ventral aorta 



Bulbus cordis 



Interventricular foramen 

 - L. horn of sinus venosus 



L. umbilical vein 

 Tail gut 



Cloaca 



Meianephric anlage 

 114 

 L. umbilical artery 



'Anastomosis between 

 dorsal aorta 



Allantoic stalk 

 L. dorsal aorta 

 Mesonephric duct 



Cephalic limb of intestinal 



Dor sal aorta ^ | Artery to mesonephros 



Mesentery Caudal limb of intestinal loop 



FIG. 105. Reconstruction of a 6 mm. pig embryo in the median sagittal plane, viewed 

 from the right side. The numbered heavy lines indicate the levels of the transverse sections 

 shown in Figs. 106-1 17. The broken lines indicate the outline of the left mesonephros and the 

 course' of the left umbilical artery and vein. The latter may be traced from the umbilical cord 

 to the liver where it is sectioned longitudinally. (Original drawing and reconstruction by 

 K. L. Vehe). X 16.5. 



posterior limb buds and from the body wall, pass cephalad in the somato- 

 pleure at each side (Fig. 72). Their course is first cephalad, then dorsad, 

 until they enter the liver. The left vein enters a wide channel, the ductus 

 venosus, which carries its blood through the liver, thence to the heart by 

 way of the right vitelline trunk. The right vein joins a large sinusoidal 



