THE ENGLISH SPARROW. 223 



Observe the thinner walls of the posterior portions of the 

 syrinx. Observe the delicate vertical semilunar mem- 

 brane projecting forward into the syrinx from the angle 

 between the bronchi. By the vibration of this membrane, 

 voice is produced. 



Note the relative position of trachea and esophagus. 

 How is the food, in passing through the mouth, kept from 

 getting into the trachea through the glottis ? 



III. Organs of Digestion. Dissect out and remove the 

 trachea and anterior ends of the bronchi. Then proceed 

 to a dissection of the digestive system, disregarding the 

 cutting of blood vessels ; for the circulatory system will 

 be studied later in an injected specimen. 



Trace the alimentary canal, beginning at the mouth. 

 The large crop, in the midst of the esophagus, is a sort of 

 food reservoir in which the comminution of ingested food 

 is begun. In its transparent walls may be seen bands of 

 muscle fibers, which, contracting, give to the crop a sort of 

 slow, churning motion ; and this, together with the grind- 

 ing action of the gravel usually found in the crop, and the 

 softening action of secretions poured from glands in its 

 walls, begins the reduction of the food. 



A short distance posterior to the crop, the backward con- 

 tinuation of the esophagus enters the mottled glandular, 

 slightly dilated stomach. 



Close behind the stomach is the large gizzard, some- 

 imes called the muscular stomach. Note the shape of 

 this organ, the satiny luster of its exterior, the thickness 

 of its powerful muscular walls, the toughness of its fibrous 

 inner coat, and the fine gravel mixed with its contents. 

 This gravel takes the place of teeth, and assists in the 

 final reduction of the food. 



The intestine immediately succeeds the gizzard. The 

 first long loop in it is called the duodenum. Into this 

 part the duct from the inclosed whitish or pinkish pan- 



