=Digestive System.=--The large mouth cavity is connected by a short throat with the gullet, or esophagus (Fig. 255). A slit called the glottis opens from the throat into the lungs (Fig. 255). Is the gullet long or short? Broad or narrow? Is the stomach short or elongated? Is the division distinct between the stomach and gullet, and stomach and intestine? Is the liver large or small? Is it simple or lobed? The pancreas lies between the stomach and the first bend of the intestines (Fig. 255). What is its shape? A bile duct connects the liver with the small intestine (_Dc_, Fig. 255). It passes through the pancreas, from which it receives several pancreatic ducts. After many turns, the small intestine joins the large intestine. The last part of the large intestine is called the rectum (Latin, straight). The last part of the rectum is called the cloaca (Latin, a drain), and into it the ducts from the kidneys and reproductive glands also open. The kidneys are large, elongated, and flat. They lie under the dorsal wall. The urinary bladder is also large. Does the salamander have a similar digestive system? (Fig. 256.) Why are the liver and lungs (Fig. 256) longer in a salamander than in a frog? [Illustration: FIG. 256.--ANATOMY OF SALAMANDER. _1a_, heart; _2_, lungs; _3a_, stomach; _3b_, intestine; _3c_, large intestine; _4_, liver; _8_, egg masses; _10_, bladder; _11_, vent.] =Respiration.=--How many _lungs_? Are they simple or lobed? (Fig. 256.) A lung cut open is seen to be baglike, with numerous ridges on its inner surface. This increases the surface with which the air may come in contact. In the walls of the lungs are numerous capillaries. Does the frog _breathe with mouth open or closed_? Does the frog have any ribs for expanding the chest? What part of the head expands and contracts? Is this motion repeated at a slow or rapid rate? Regularly or irregularly? There are valves in the nostrils for opening and closing them. Is there any indication of opening and closing as the throat expands and contracts? The mouth and throat (pharynx) are filled with air each time the throat swells, and the exchange of gases (which gases?) takes place continually through their walls and the walls of the lungs. At intervals the air is forced through the glottis into the lungs. After a short time it is expelled from the lungs by the muscular abdominal walls, which press upon the abdominal organs, and so upon the lungs. Immediately the air is forced back into the lungs, so that they are kept filled. In some species the lungs regularly expand at every second contraction of the throat. This is shown by a slight outward motion at the sides. Does the motion of the throat cease when the frog is under water? Why would the frog be unable to breathe (except through the skin) if its mouth were propped open? Why does the fact that the breathing is so slow as to almost cease when hibernating, aid the frog in going through the winter without starving? (Chap.