324 



THE DOGFISH. PHYLUM CHORD AT A 



botweon the gill slits, are known as visceral arches and have the 

 same names as the skeletal arches which they contain (p. 319). 

 Each contains also arteries and nerves. The movements of the 

 visceral arches, which carry out the processes of feeding and, 

 as we shall see, of breathing, are brought about by muscles 

 which run between the cartilages of the arches and the coracoid 

 region of the shoulder girdle. The pharynx passes into the 

 narrower cesophagus which lies in the peritoneal cavity and soon 

 merges into the stomach (Fig. 244). The cardiac portion of this is 

 an elongated sac ; near its hinder end on the right side the narrow 

 tubular pyloric division arises and runs forw^ards beside the 

 cardiac. A slight constriction at the anterior end of this marks 



the presence of the pyloric sphincter which 

 divides it from the intestine. The first part 

 of this is a short narrowish duodenum 

 which receives the ducts of the liver and 

 pancreas. Behind this is the ileum, which is 

 long and wide and directed backwards, and 

 has its internal surface increased by a spiral 

 fold of the mucous membrane known as the 

 spiral valve (Fig. 245) ; its hinder end opens 

 into a narrow rectum without a spiral valve. 

 This in turn ends in a wider cloaca, which 

 receives the urinary and genital ducts and 

 opens by the vent. 



The liver is a very large organ, consisting 

 of long right and left lobes united in front and slung by the 

 suspensory ligament from the anterior wall of the peritoneal 

 cavity. The gall bladder is embedded in the front part of the 

 left lobe of the liver, but usually a part of it shows upon the 

 surface. From it the bile duct runs backwards to open into the 

 intestine, lying in the membrane or omentum which carries 

 the hepatic artery and portal vein. The pancreas lies between the 

 stomach and intestine ; it is long and narrow and has in front 

 a rounded ventral lobe, from which its duct passes to the ventral 

 side of the intestine. The rectal gland is a small, cylindrical 

 structure which opens into the dorsal side of the rectum by 

 a duct. The spleen, which has no functional connection wdth the 

 alimentary canal, is a triangular body attached by a membrane 

 to the hinder end of the stomach, with a prolongation running 

 fni-vqrd along the right side of the pyloric division. 



Fig. 245. — Diagram of 

 spiral valve. — After 

 T J. Parker. 



