332 ELEMENTARY ZOOLOGY 



certain large air-sacs in the abdomen, which communicate 

 with them. 



Beneath the trachea note the long oesophagus. Inflate 

 the oesophagus with a blowpipe and note how distensible 

 is its lower end near the breast. This distensible portion 

 is called the crop. If the alimentary canal be drawn out 

 straight the oesophagus will be found to run as an almost 

 straight tube down the left side of the body to the gizzard. 

 This latter organ has very thick muscular walls and in it 

 the food is ground up among the small bits of gravel it 

 contains. Extending from the gizzard near the entrance 

 of the oesophagus note the long pyloric loop of the intes- 

 tine called duodenum. Within this loop is a long pinkish 

 gland, the pancreas, which empties by a duct into the 

 duodenum. Into the duodenum also the overlying liver 

 empties its secretion of bile from the median-placed gall- 

 bladder. From the duodenum the small intestine or ileum 

 extends with many convolutions to its exit through the 

 cloacal aperture. On the intestine near the cloaca! open- 

 ing note a pair of glandular structures, the cceca. The 

 short part of intestine between the caeca and cloaca is 

 called the rectum. On the left side of the body beneath 

 the gizzard note a dark glandular structure, the spleen. 



Make a drawing of the dissection as so far worked out. 



TECHNICAL NOTE Remove the alimentary canal, cutting it free 

 posteriorly at the caeca and anteriorly just above the muscular gizzard. 

 Cut open the gizzard and note its structure. The contained sand 

 and gravel grains are picked up by the bird as it eats. 



On either side of the throat note the well-defined thyroid 

 gland ; in young sparrows will be noted on each side cf 

 the neck a mass of tissue, the remains of the thymus 

 gland, which disappears in the adult. 



Cut transversely through the lower end of the heart and 

 note that the ventricles are wholly distinct, whereas in the 

 toad and snake they are incompletely separated In the 



