32 



Basic Structure of Vertebrates 



POST CAVA VEIN 



CUT EDGE OF 

 PERITONEUM 



QUADRATE LOBE' 



GALL BLADDER/ 



Fig. 25. The human liver viewed from below. (After Sobotta. Courtesy, Neal and 

 Rand: "Chordate Anatomy," Philadelphia, The Blakiston Company.) 



^'STOMACH 



DUCT OF SANTORIN 

 RSAL PANCREAS 



DORSAL PANCREAS 



VENTRAL PANCREAS 

 DUODENUM 



WIRSUNG'S DUCT 



EARLIER STAGE 



LATER STAGE 



Fig. 26. Two stages in the development of the pancreas. The duct of the dorsal 

 pancreas, Santorini's duct, may degenerate in ontogenesis. The two embryonic 

 glands unite into a single organ in the adult. (After Broman. Courtesy, Neal and 

 Rand: "Chordate Anatomy," Philadelphia, The Blakiston Company.) 



gion, instead of being an open lumen, is largely filled by so-called 

 "central cells" differing from the typical pancreatic secretory cells 

 which constitute the wall of the alveolus (Fig. 29). The central cells are 

 of doubtful significance. Scattered irregularly among the pancreatic 

 alveoli are solid masses of cells which exhibit peculiar reactions to his- 

 tologic dyes. They are known as "islands of Langerhans" (Fig. 29). 

 The liver is a conspicuous organ in all vertebrates, but there is 

 doubt as to the existence of a pancreas in some fishes. Pancreatic tissue 

 has been found buried within the liver or imbedded in the wall of the 

 intestine of some fishes. This occasional concealment of the pancreatic 



