310 ZOOLOGY 



hand and foot considerably modified from those of an animal which uses 

 all the appendages for locomotion. The digestive tract is also much like 

 that of man. (See page 330.) 



Organs of Digestion. — The digestive glands, and the salivary, gastric, 

 intestinal, and pancreatic glands have nearly all the same position and 

 functions. The glands which act upon starch are better developed in the 

 rabbit than in man because of the predominance of starchy foods used by 

 the rabbit. The intestine is longer than in flesh-eating animals. 



Circulation. — In all mammals (of which the rabbit is an example) the 

 blood in its circulation passes through a four-chambered heart. There is a 

 system of closed blood tubes which, according to the position and function, 

 are named arteries, veins, and capillaries. The whole process of circulation 

 is identical with that process in man (see Circulation, page 350). The 

 lungs and heart are separated from the lower part of the body cavity by 

 means of a thin -walled plate of muscle, called the diaphragm. This dia- 

 phragm occurs in all mammals. 



Oxygen is taken up by the blood and respiration takes place in a similar 

 manner to that process in man. 



In like manner the organs of excretion of nitrogenous waste, the skin and 

 kidneys, eliminate the waste from the body in the same manner as it is done 

 in man. 



Nervous System. — The brain and central nervous system of the rabbit 

 are well developed. A brain, which has a large cerebrum and other char- 

 acteristics of the brain of man, supplies sense organs through twelve cranial 

 (brain) nerves (see The Nervous System, page 400) . The senses, especially 

 those of sight and hearing, are also highly developed and are very acute. 

 We have seen that the eyes are so placed that the animal is able to look to 

 the sides and behind without turning the head. Organs of taste, the taste 

 buds, such as are found in man, are also developed in the rabbit. The sense 



of touch appears to be well developed 

 over the entire body, but is especially 

 keen in the region of the nose (see 

 The Senses, page 419). 



Characters of Mammals. — 

 Vertebrate animals which have a 

 The common house rat. From photograph, hairy coat and which nurse the 



about one fourth natural size. y^^^^^ ^^ ^^^^^ ^f milk-produc- 



ing glands (the mammary glands) are called mammals. Such evi- 

 dently is the rabbit. Rats, woodchucks, cattle, dogs, cats, and 

 man are all examples of this group. Man is by far the best men- 

 tally developed of all this group and is therefore spoken of as the 

 highest of the mammals. 



