ORGANS OF DIGESTION. 381 



from the moist condition of their food, the liquid element 

 they inhabit, and their want of masticating organs, they are 

 generally destitute of salivary glands. The mouth is copi- 

 ously provided with mucous follicles. From the want of 

 means of dividing their food the oesophagus is short and 

 wide to receive it entire, and is bounded below by the circular 

 fibres of the strong cardiac sphincter. The oesophagus is 

 often marked internally with regular longitudinal folds which 

 greatly extend the surface of the mucous coat, and is some- 

 times also provided with rudimentary teeth, like the cu- 

 taneous spines often developed on the surface of the body. 

 The rudimentary salivary glands appear to be most distinct 

 where the pancreatic are least developed, and the increased 

 size and number of the buccal muciparous glands generally 

 compensate for the want of salivary glands in this class. A 

 small valvular fold, or rudimentary velum palati, seen as low as 

 the lampreys, and most developed above, as in the zeiis, com- 

 monly assists in conveying the food and water backwards to 

 the pharnyx, from which the water passes out freely between 

 the branchial arches, and the food is directed to the oesophagus 

 by the teeth of the pharyngeal bones, which are the most 

 constant teeth of fishes and the most analogous to the 

 gastric dental organs so common in the inverteb rated classes. 

 The alimentary canal of fishes is generally more short 

 and simple than in higher vertebrata, which accords with 

 their predaceous habits and with their inferior position in 

 the scale. With a short infundibuliform oesophagus, and 

 a capacious gastric cavity with its two orifices approximated, 

 the whole digestive canal of fishes is often shorter than 

 the trunk, and passes nearly straight through the body, 

 as seen in the herring, clupea harengus (Fig. 123. A.), where 

 the narrow cordiac part of the oesophagus (] 23. A. a.) opens 

 into a lengthened tapering stomach (123. A. b.) commu- 

 nicating by a long ductus pneumaticus (123. A. m.) with 

 a large fusiform air-sac (123. A. /. /.), and where the wide 

 duodenum (123. A. c.) provided with numerous pancreatic 

 tubuli (123. A. d. d.) forms the commencement of a short 

 intestine (123. A. e. e.) which opens into the cloaca (123. 

 A. /.) anterior to the aperture (123. A k.) of the urinary 

 organs and of the vas deferens (123. A. i) from the testes 

 (123. h. h.) of the male and the corresponding opening of 

 the ovaries in the female. 



