THE DOGFISH 353 



of a gill, known as a pseudobranch. The regions between 

 the clefts, and those immediately in front of the first cleft (the 

 spiracle) and behind the last, are known as visceral arches, 

 and named, in order, mandibular, hyoid, and first to fifth 

 branchial. Each contains a skeletal arch, arteries, and a 

 nerve (Fig. 271). The spiracle separates the mandibular and 

 hyoid arches. The gills are respiratory organs. In life the 

 fish is continually taking in water at the mouth and passing 

 it out over the gills and through the clefts by a munching 

 action of the lower jaw. From the pharynx the narrower 

 oesophagus leads back through the ccelom to the stomach. 

 This is sharply divided into a cardiac and a pyloric part. 

 The former is a sac, in shape not unlike the stomach of 

 the frog ; near its hinder end on the right side arises the 

 narrow tubular pyloric division, which runs forwards beside 

 the cardiac. At its front end a slight constriction marks the 

 presence of the pyloric sphincter and divides it from the 

 intestine. The main part of this is a long, wide sac, known 

 as the ileum, which passes backwards towards the cloaca 

 and has its internal surface increased by a spiral fold of 

 the mucous membrane known as the spiral valve. Between 

 this region and the pyloric sphincter lies a short, somewhat 

 narrower region called the duodenum or bursa entiana, 

 which is without a spiral valve and receives the ducts of 

 the liver and pancreas. At its hinder end the ileum 



Fig. 252.— A female dogfish in which the abdominal and pericardial 

 cavities have been opened from the ventral side, and the viscera 

 somewhat displaced. The pericardium has been opened slightly 

 to the left of the middle line, and the right lobe of the liver has 

 been cut away. 



al/.p., Abdominal pores; /'..bile duct; c, cardiac limb of stomach; car., caudal 

 artery; c.v., caudal vein; d., bursa entiana \f.l., falciform ligament, with the 

 internal opening of oviducts ; g.b., portion of gall bladder appearing on surface 

 of left lobe of liver in which it is embedded ; z\, intestine ; i.a. t intestinal branch 

 of anterior mesenteric artery; /., lienogastric artery; not., notochord ; ov. t 

 ovary; p., portal vein lying beside hepatic artery; ps., pancreas with duct 

 opening into intestine ; pp., pyloric limb of stomach ; r., rectum, between 

 hinder ends of oviducts, with rectal gland {r.gl.) attached to its dorsal side; sh., 

 right shell gland on course of right oviduct; sp., spleen; sp.c., spinal cord; 

 ur.p. , urinary papilla ; v. , branch of portal vein formed by junction of intestinal 

 and splenic veins. 



Besides the above, note — nostrils; oronasal grooves; mouth; pectoral and pelvic 

 fins ; pericardial and abdominal cavities ; heart, consisting of sinus venosus 

 (behind), ventricle, auricle (showing at sides of ventricle), and conus ; cloaca, 

 and transverse section of tail, showing at the sides the myomeres, above the 

 anterior dorsal fin, and in the middle the cartilage of the backbone enclosing 

 spinal cord, otochord, and blood vessels. 



