xii PHYLUM CHORDATA 375 



the liver, the bile duct, runs from the liver to the intes- 

 tine. Proximally it is connected with the gall-bladder and 

 by branch ducts with the right and left lobes of the liver. 

 It opens into the commencement of the colon. 



The pancreas (pan) is a light-coloured compressed gland 

 consisting of two main lobes with a broad connecting isthmus 

 lying in the angle between the right-hand limb of the stomach 

 and the small intestine. Its duct enters the wall of the small 

 intestine and runs in it for about half an inch, opening event- 

 ually at the point where the small intestine passes into the 

 colon. 



Connected with the rectum on its dorsal aspect is an oval 

 gland, the rectal gland (ret.gl), about three-quarters of an 

 inch in length. 



The spleen (spl) is a dark-red or purple body attached to 

 the convexity of the U-shaped stomach, and sending a narrow 

 lobe along the right-hand limb. 



The organs of respiration in the dogfish are the gills, 

 situated in the five gill-pouches. Each gill-pouch is an 

 antero-posteriorly compressed cavity opening internally into 

 the pharynx and externally by the gill-slit. The walls of the 

 pouches are supported by the branchial and hyoid arches with 

 their rays, the first pouch being situated between the hyoid 

 and first branchial arches, the last between the fourth and 

 fifth branchial arches. On the anterior and posterior walls 

 of the pouches are the gills, each hemibranch consisting of a 

 series of close-set parallel folds or plaits of highly vascular 

 mucous membrane. Separating adjoining gill-pouches and 

 supporting the gills are a series of broad interbranchial septa, 

 each containing the corresponding branchial arch with its 

 connected branchial rays. The most anterior hemibranch is 

 borne on the posterior surface of the hyoid arch. The last 

 gill-pouch differs from the rest in having gill-plaits on its 



