628 



THE DIGESTIVE SYSTEM 



caudal aspect of the septum. The ends achieved in the human and pig embryos 

 are much the same, therefore, and the anterior face of the developing liver 

 and the septum transversum are intimately associated. 



3) Development of the Rudiments of the Pancreas: a) Shark Embryo. 

 In the embryo of Squalus acanthias, the shark, the pancreas arises as a dorsal 

 diverticulum of the gut a short distance posterior to the gallbladder and hepatic 

 outpushings (fig. 279B). It grows rapidly and, in the 18- to 20-mm. embryo, 

 it is a much-branched gland with its pancreatic duct entering the duodenum 

 slightly anterior to the beginning coils of the spiral valve. 



b) Frog Embryo. In the frog, the pancreas arises from three diverticula, 

 one dorsal and two ventral, near the liver rudiment (Kellicott, '13, p. 167). 

 The dorsal diverticulum is solid and separates from the gut tissue. The two 

 ventral diverticula arise together from the ventral portions of the gut but soon 

 branch into two rudiments. As these rudiments enlarge and branch, they 

 eventually unite with the dorsal diverticulum of the pancreas, and the three 

 fuse to form one gland. The proximal portion of the original, ventral, pan- 

 creatic outpushing remains as the pancreatic duct and empties into the 

 duodenum close to the bile duct. 



c) Chick Embryo. As in the frog, three pancreatic diverticula arise in the 



Fig. 297. Developing coils in the digestive tube of the pig. (A) 12 mm. embryo. 

 (B) 24 mm. embryo. (C) 35 mm. embryo. (D) Cecum and large intestine showing 

 coils in 120 mm. embryo. (E) Coiling of large intestine of young adult pig. Observe 

 haustra or lateral diverticula of colonic wall. (All figures redrawn and modified from 

 Lineback, 1916, Am. J. Anat. 16.) 



