266 HUMAN EMBRYOLOGY AND MORPHOLOGY. 



218). It may represent a modified lobule of the liver. In some 

 animals it is absent. The cystic duct represents the stalk of the 

 bud. 



The Oesophagus and Stomach. — The Oesophagus in a third 

 week's foetus is the junctional piece of fore-gut that unites the 

 pharynx to the scarcely differentiated stomach (Fig. 202, p. 244). 

 It is extremely short, but with the development of the lungs and 

 recession of the diaphragm it becomes elongated. In the foetus 

 the mucous membrane is thrown into four longitudinal folds 

 which end abruptly at the orifice of the stomach in a circular 

 epithelial ridge which sometimes persists and acts as a valve 

 at the cardiac orifice of the stomach. These four ridges can 

 be seen in adult apes. At one stage of development the cervical 

 part of the oesophagus is filled with epithelium and thus closed. 



The Stomach. — The stomach is developed out of that part of 

 the fore-gut which lies between the oesophagus and pharynx 

 in front and the yolk sac, duodenum and liver bud behind 

 (Fig. 187, p. 229). At first it is contained in that part of the 

 primitive mesentery to which the name of septum transversum 

 has been given, and is situated below the lower cervical and 

 upper dorsal region of the spine (Fig. 204). In the 3rd week 

 the gastric part of the fore-gut shows a dorsal bulging — the 

 greater curvature. As the liver and gut are developed, 

 the stomach separates itself from the septum transversum 

 and comes to be suspended from the dorsal wall of the 

 coelom by the dorsal mesogastrium (Fig. 213 A). The gastro- 

 hepatic omentum is part of the ventral mesogastrium. The 

 oesophageal end of the stomach is fixed in the septum trans- 

 versum (diaphragm) ; the outgrowth of the liver bud fixes its 

 pyloric end in the ventral mesogastrium. Three changes 

 quickly ensue, the one being partly dependent on the other : 



(1) Its dorsal margin grows rapidly so as to produce the 

 greater curvature ; this growth particularly affects the left side 

 of the cardiac end of the stomach and thrusts the attachment of 

 the dorsal mesogastrium towards the right side at the cardiac end 

 of the stomach. The greater part of the fundus or cardiac sac of 

 the stomach is produced from the left side. 



(2) The dorsal mesogastrium being too limited in extent to 

 allow for the growth of the greater curvature, the stomach 



