378 ORGANS OF DIGESTION. 



tubuli (122. D. e.) encompass the hepatic ducts, and open 

 into them by oblique valvular apertures directed downwards. 

 These glands, which are common to the naked tentaculated 

 cephalopods of both sexes, were mistaken by Swammerdam 

 and Monro for generative organs, but by their structure and 

 anatomical relations, they must be regarded as the analogues 

 of the pancreas 'of other classes : they present vesicular 

 enlargements at the ends of their tubuli like those of the 

 pancreatic and salivary glands of most other animals, and 

 part of their lobules sometimes terminate by separate ducts 

 (122. D.) in the cavity of the spiral stomach. By the exten- 

 sion of the valvular folds (122. D. d.) from the entrance of 

 the hepato-pancreatic duct along the course of the intestine, 

 the secretions of these glands may also mingle with the food 

 beyond the pyloric orifice of the stomach, as in vertebrated 

 classes ; and in the empty and collapsed state of these parts 

 the bile may pass along this valvular groove towards the 

 anus without entering the stomach or duodenum in these 

 carnivorous mollusca still destitute of a gall-bladder. 



FIFTH SECTION. 



Digestive Organs of the Spini- Cerebrated or Vertebrated 



Classes. 



THE high development of all the organs and systems of ver- 

 tebrated animals, and the intricate constitution of all their 

 tissues and fluids require a corresponding complexness in 

 their digestive apparatus to produce those physical and 

 chemical changes of the food which are necessary for its 

 perfect assimilation to their complex bodies. Their alimen- 

 tary canal is extended between the spino-cerebral axis and 

 the heart, and terminates by distinct buccal and anal orifices 

 without perforating the nervous axis. It is always provided 

 with a distinct gastric enlargement, and with a large conglome- 

 rate liver, a spleen, and a pancreas. The hepatic and pancreatic 

 secretions are always poured into the intestine below the 

 pyforic orifice of the stomach, and the colon is generally 

 distinguishable from the more narrow anterior portion of 

 the intestine. The ossophageal portion of the alimentary 



