Digestive system of scoliodon

🦈The digestive system consists of the alimentary canal and the digestive glands.

 🦈The alimentary canal 

starts with the mouth and terminates in the cloaca. 

🦈The mouth leads into a spacious buccal cavity which 

is lined with mucous membrane.

🦈The floor of the buccal cavity becomes folded to form a non-muscular and non-granular ‘tongue’. 

🦈The mucous membrane is very thick and rough due to the presence of dermal denticles or teeth. 

🦈The teeth are very sharp and are obliquely placed . 

🦈The teeth are homodont i.e., the teeth are similar in shape and polyphyodont ie posesses several sets of teeth functioning in succession.

 🦈The buccal cavity leads into pharynx. 

🦈On either side of the pharynx there lie the internal openings of  the spiracles and five branchial clefts. 

🦈The mucous membrane of the pharyngeal wall contains 

numerous dermal denticles. 

🦈The pharynx leads into a narrow oesophagus. 

🦈The inner mucous membrane of the pharynx is raised to form longitudinal folds.

🦈 The oesophagus dilates posteriorly to form a large stomach. 

🦈The stomach is highly muscular and is bent on itself to form a J-shaped configuration. 

🦈The long limb of the stomach is continuous with the oesophagus and the shorter one passes into the intestine. 

🦈The entrance of the oesophagus into the 

stomach is provided with a crescentic fold which serves as the valve.

 🦈The long anterior limb is called the cardiac stomach and the short posterior limb is designated as the pyloric stomach. 

🦈A small outgrowth often called ‘blind sac’ is present at the junction of the cardiac and 

pyloric limbs.

🦈The inner lining of the cardiac stomach is folded longitudinally like that of oesophagus  

🦈The internal lining of the pyloric stomach is mostly smooth though slight foldings are observed at the distal end.

🦈The pyloric valve, at the end of the pylorus, guards the entrance of it into a thick-walled small  chamber called the bursa entiana. 

🦈The bursa entiana is immediately followed by wide tubular intestine which becomes narrowed posteriorly as the rectum. 

🦈The rectum opens into the cloaca. 

🦈A tubular caecal or rectal or digit form gland opens into the rectum.

🦈The inner surface of the intestine becomes folded to form an anticlockwise spiral of approximately two and a half turns. 

🦈This is called the scroll valve which increases the absorptive surface of the intestine and also checks the rapid flow of digested food through the intestine.

🦈The major digestive gland is the liver which is a massive yellowish gland and consists of two lobes. 

🦈The lobes are united anteriorly. 

🦈A thin-walled V-shaped gall-bladder is present in the anterior part of the right lobe of liver. 

🦈The bile duct receives a few smaller ducts from the two lobes of the liver and opens 

into the anterior end of intestine near the commencement of the scroll valve.

🦈The pancreas is a pale compact irregular body and consists of a dorsal lobe situated parallel to the 

posterior part of cardiac stomach and a ventral lobe which remains closely attached to the pyloric stomach. 

🦈The pancreatic juice is poured into the intestine by pancreatic duct situated opposite to the aperture of the bile duct.

🦈The functional significance of rectal gland is not properly known. 

🦈The *rectal gland* has a central cavity lined with cuboidal cells. 

🦈It is highly vascular and composed of lymphoid tissue. 🦈It discharges a fluid 

into the lumen of the intestine but its actual role is not known.

🦈The buccal cavity possesses no salivary glands.