188 AVES (the bird) 



(b) Identify and describe the two auricles and the two 



ventricles. 



(c) Snip off the apex of the heart with a pair of scissors 



and observe the cavities of the two ventricles. 

 Note the difference (1) in shape, and (2) in thick- 

 ness of walls. Explain. 

 6. The Digestive System. 



(1) Mouth. 



(a) Size? 



(b) Shape? 



(c) Beaks for teeth. Why? 



(2) The Pharynx opens' into the gullet. 



(3) The Gullet. 



(a) Is the gullet, or esophagus, the same size all the way 



to the gizzard? Can the pigeon swallow with its 

 head down? 



(b) What is the first enlargement called? Of what use 



is the crop? 



(c) The glandular stomach is the slight enlargement near 



the gizzard. What is its size compared with that 

 of the crop? If the opening into the gizzard 

 were closed, could fluids pass from the glandular 

 stomach into the intestine? 



(4) The Gizzard. 



(a) Of what use is the gizzard, or muscular stomach? 



(b) Make a cross-section through the gizzard. 



(c) Of what does it consist? 



(d) Character of the lining? 



(e) What does it contain? 



(f) How many openings has the gizzard, and into what? 



(g) Can the opening from the glandular stomach be 



closed? 

 (h) Is the gizzard cecal? 



(5) The Duodenum. The first loop of the intestine is 



called the duodenum. 



(a) How and by what is it held in position? 



(b) From what is the intestine suspended? 



(c) Note the veins and arteries in the mesentery. 



