382 



ORGANS OF DIGESTION, 

 FIG. 122. 



The oesophagus of fishes, surrounded by an exterior circular 

 and an inner longitudinal layer of muscular fibres, and with a 

 white villous plicated mucous coat provided with numerous 

 distinct muciparous follicles, often terminates imperceptibly 

 in the capacious stomach, and sometimes the pyloric end of 

 the stomach passes insensibly into the duodenum, as in the 

 short straight simple alimentary canal of the lamprey. The 

 wide membranous cardiac portion of the stomach (123. A. b.) 

 is commonly directed backwards as a simple closed sac, and 

 the stronger narrow muscular pyloric part (123. A. c.) ap- 

 proaching in thickness to a gizzard, extends forward and 

 to the right side. This gastric sac is sometimes globular as in 

 the lophius, or extended backwards as in the polypterus and 

 the xiphias ; but the cardiac and pyloric orifices are almost 

 always approximated, so that the food is retained as in a 

 coscum continued straight from the mouth. The muscular 

 bands of the cardiac and pyloric sphincters are strongly marked, 

 the pylorus is strengthened by a cartilaginous layer between 

 the mucous, and the muscular tunics, and the mucous coat 

 around the pyloric orifice extends inwards to form a circular 

 valve, with a fibriated margin, at the commencement of the 

 duodenum as in many of the mollusca. The excretory ducts of 

 the liver and pancreas enter the duodenum immediately beyond 

 the pyloric valve, and the variously plicated mucous lining of 



