THE DOMESTIC PIGEON 367 



The Digestive System. The mouth is without teeth. Sali- 

 vary glands opening into the mouth furnish a fluid which 

 assists in swallowing the food. There is a large tongue 

 (Fig. 191, 7), pointed at its anterior end. From the pharynx 

 there are openings (Fig. 191, 6) to the nostrils and to the 

 ears, as in reptiles and amphibians. A short oesophagus 

 (Fig. 191, 8, 10) leads to a large crop (Fig. 191, 9), in which 

 the food, consisting largely of grain, is somewhat softened 

 before passing into the glandular stomach (Fig. 191, 11) behind 

 it. Glands in the lining walls of the stomach pour out a 

 digestive fluid which serves to further soften the food, 

 which then enters the gizzard (Fig. 191, 12), an organ with 

 a yellow, horny lining surrounded by a thick mass of muscle. 

 The gizzard contains small stones swallowed for the purpose 

 of assisting in grinding the food ; this process is accomplished 

 by movements of the muscular walls. Beyond the gizzard 

 the small intestine (Fig. 191, 13) forms a loop inclosing the 

 pancreas (Fig. 191, 17), which discharges its secretion into 

 the intestine through three ducts, one of which is shown in 

 Fig. 191, 18. The liver (Fig. 191, 14) is large and opens into 

 the intestine by two bile-ducts (Fig. 191, 15, 16). At the pos- 

 terior end the intestine (rectum) passes without change of 

 diameter into the cloaca (Fig. 191, 20). The junction between 

 the rectum and cloaca is marked by the presence of two cceca 

 (Fig. 191, 19). The spleen (Fig. 191, 21) is bright red, and is 

 attached to the walls of the glandular stomach. 



The Circulatory, Respiratory, and Excretory Systems. The 

 heart is a large, four-chambered organ inclosed in the peri- 

 cardium (Fig. 191, 22). It consists of two auricles and two 

 ventricles, the latter separated by a complete partition, as in 

 the crocodilians. The circulation is double, and the aerated 

 and non-aerated blood come nowhere in contact, except in 

 the capillaries. The blood is sent to the lungs from the right 

 ventricle, through the pulmonary artery (Fig. 191, 29). Freed 



