ANATOMY OF A 17.8 MM. HUMAN EMBRYO 79 



pairs of dorsal intersegmentals have lost their connection with the 

 dorso-median aorta. They are now connected with the sub- 

 clavian arteries by the precostal anastomosis which forms the 

 adult superior intercostal. 



Visceral arteries. The ventral visceral arteries and the lateral 

 visceral arteries of the right side are indicated in plate 1. 



In the thorax several small, ventral visceral arteries (Aa.oe.) 

 extend from, the aorta through the mediastinum to the oesophagus. 

 According to Broman ('08) these oesophageal arteries are of 

 secondary formation, the primary segmental arteries having early 

 disappeared. 



The coeliac artery (A.coel.) leaves the aorta slightly caudad 

 of the 11th thoracic pair of dorsal intersegmental arteries. It 

 extends between the medial surfaces of the anlagen of the supra- 

 renal glands, and entering the mesogastrium at once gives off the 

 left gastric artery which turns cephalo-ventrally. The coeliac 

 then continues in the mesogastrium (hidden in the reconstruction 

 by the stomach, Ga.), and having given off the splenic artery it 

 becomes the hepatic. The former artery extends in the meso- 

 gastrium to the splenic anlage; the latter enters the lesser omen- 

 tum and divides into the hepatic artery proper and the gastro- 

 duodenal. The hepatic proper can be seen in the reconstruction, 

 entering the liver just ventral to the portal vein (V.P.). It gives 

 off the small cystic branch (not shown in the reconstruction) 

 which accompanies the cystic duct. The gastro-duodenal artery 

 can be traced distally between the left side of the duodenum and 

 the proximal part of the dorsal pancreas, 



Tandler ('03) finds that the coeliac artery in a 17 mm. human 

 embryo arises from the aorta slightly above the level of the 20th 

 intersegmental (12th thoracic) artery. 



The superior mesenteric artery (A.mes.s.) takes origin from 

 the aorta approximately on a level with the 12th thoracic pair 

 of dorsal intersegmental arteries. It extends ventrally between 

 the caudal ends of the suprarenal glands (plate 4) into the dorsal 

 mesentery. It courses to the left of the duodenum and passes 

 dorsal to the vena omphalomesenterica. In the dorsal mesen- 

 tery it gives off numerous small branches, and crosses on the right 



