AVES 2G7 



of the proventriculus. Following the gizzard is the duodenum. 

 The pancreas is in a loop of the duodenum and pours its secre- 

 tion into it. The large liver pours its bile into the duodenum. 

 The ileum continues from the duodenum to the large, straight 

 intestine, the rectum. The junction is marked by long, blind 

 pouches or ceca. The large intestine ends in an enlargement 

 called the cloaca, or sewer, because it receives the undigested 

 food, the excretions of various organs, and the eggs, all of which 

 pass out l)y one external opening. 



Circulatory System. — Circulation is complete. The heart is 

 large and composed of two auricles and two ventricles. The 

 right aortic arch persists in birds, while the left persists in man. 

 The circulation is double, pulmonary and systemic. The sep- 

 tum is complete between the ventricles, thus keeping the impure 

 blood (venous) from the pure blood (arterial). 



The Respiratory System. — The pharynx opens by the glottis 

 into the trachea, which divides and sends ramifying branches into 

 the lungs. The lungs connect with the system of air-sacs which 

 aid the bird in flight. "Usually five pairs of these sacs are pres- 

 ent, largely in the coelom, but extending in between the muscles 

 (breast and axillary region) and also into the bones. "^ The 

 syrinx or voice-box is at the junction of the bronchial tubes 

 and the trachea, where they enlarge to form it. This syrinx 

 is especially well-developed in singing birds. 



Many of the bones are hollow and filled with air. Thus is 

 the inspired air distributed over the body, so that the aeration of 

 the blood is not confined to the limited area of an orchnary organ 

 of respiration. The bird is a very warm-blooded animal, and to 

 keep up its heat it must use oxygen rapidly. This it does by its 

 rapid breathing, which may be at the rate of sixty per minute. 

 The temperature of birds is from 100° to 110° F., while in man 

 the temperature is 98.6° F. The temperature is also kept up by 

 the non-conducting feathers and by the absence of skin glands, 

 with the exception of the oil gland at the base of the tail. 



In the absence of a diaphragm, expiration is effected by the 

 drawing of the sternum toward the spinal column and the bend- 

 ing of the hinged ribs. Inspiration is effected by the straighten- 

 ing of the ribs brought about by relaxing the muscles. Thus the 

 * Hertwig. 



