BIRDS 275 



more rapid in them than in man, and the temperature of 

 the blood is higher than in any other animals. 



Respiratory system of the sparrow. — '■ In keeping with 

 the active circulation of the blood, the respiration of the 

 sparrow is also very rapid. The lungs are fastened to the 

 dorsal walls of the body cavity and fit closely between the 

 ribs. Connected with the lungs are certain large air sacs 

 in the abdominal cavity. Moreover, many of the bones 

 of the sparrow are hollow and contain air spaces connected 

 with the lungs. 



Excretory system. — The main excretory organs are the 

 kidneys, which are fitted into the spaces between the bones of 

 the back in the posterior part of the body cavity. They are 

 tri-lobed and discharge their excretions into the cloaca 

 with which they are connected by slender ureters. 



Nervous system. — The brain is well developed and the 

 anterior part consists of two large, smooth, pear-shaped 

 bodies, the cerebral hemispheres, which constitute the cere- 

 brum. The olfactory lobes project from the anterior ends 

 of these hemispheres. Directly posterior to the cerebrum 

 and on a middle line is the transversely furrowed cere- 

 bellum. On the ventral side of the brain are the two optic 

 lobes. From the brain, the spinal cord runs throughout 

 the length of the backbone, giving off nerves to all parts 

 of the body. The nervous system of a bird is relatively 

 large. 



Senses of the sparrow. — The nostrils of the sparrow are 

 at the base of the upper mandible of the beak and open into 

 the mouth. Yet we are not sure that a bird has a very keen 

 sense of smell. On the other hand, we are positive that 

 the sparrow has a well-developed sense of sight. This is 

 true of all birds, especially of eagles and hawks. The eye 



