Section 4. the Alimentary Canal of the Dog-Fish, Is a Simple Tube

thrown into a Z shape. The mouth is rough with denticles, and has a fleshy immovable tongue on its floor. In the position of the Eustachian tube there is a passage, the spiracle (sp.), running out to the exterior just external to the cartilage containing the ear. The pharynx communicates with the exterior through five gill slits (g.s.), and has, of course, no glottis or other lung opening. There is a wide oesophagus passing into a U-shaped stomach (st.), having, like the rabbit's, the spleen (sp.) on its outer curvature. There is no coiling small intestine, but the short portion, receiving the bile duct (b.d.) and duct of the pancreas (pan.), is called the duodenum (d'dum.). The liver has large left (L.lv.) and right lobes, and a median lobe (M.lv.), in which the gall bladder (g.bl.) is embedded. The next segment of the intestine is fusiform, containing a spiral valve (Figure 4), the shelf of which points steeply forward; it is sometimes called the colon (co.). It is absorptive in function and probably represents morphologically, as it does physiologically, the greater portion of the small intestine. A rectal gland (r.g.) opens from the dorsal side into the final portion of the canal (rectum).