MAMMALS 297 



the organs of taste. The esophagus is always a simple straight 

 tube, but the stomach varies greatly, being usually simple, but 

 sometimes, as in the ruminants and whales, divided into 

 several distinct chambers. The intestine in vegetarian animals 

 is very long, being in a cow twenty times the length of the 

 body. In the carnivores it is comparatively short in a tiger, 

 for example, but two or three times the length of the body. 



The blood. of mammals is warm, having a temperature of 

 from 35 C. to 40 C. (95 F. to 104 F.). It is red in color, 

 owing to the reddish-yellow, circular, non-nucleated blood- 

 corpuscles. The circulation is double, the heart being com- 

 posed of two distinct auricles and two distinct ventricles. 

 Air is taken in through the nostrils or mouth and carried 

 through the windpipe (trachea) and a pair of bronchi to the 

 lungs, where it gives up its oxygen to the blood, from which it 

 takes up carbon dioxide in turn. At the upper end of the 

 trachea is the larynx, or voice-box, consisting of several car- 

 tilages attaching by one end to the vocal cords and by the 

 other to the muscles. By the alteration of the relative position 

 of these cartilages the cords can be tightened or relaxed, brought 

 together or moved apart, as required, to modulate the tone 

 and volume of the voice. 



The kidneys of mammals are more compact and definite in 

 form than those of other vertebrates. In all mammals except 

 the Monotremes (duckbills, etc.), they discharge their product 

 through the paired ureters into a bladder, whence the urine 

 passes from the body by a single median urethra. Mammary 

 glands, secreting the milk by which the young are nourished 

 during the first period of their existence after birth, are present 

 in both sexes in all mammals, though usually functional in the 

 female only. 



The nervous system and the organs of special sense reach 

 their highest development in the mammals. In them the 

 brain is distinguished by its large size, and by the special pre- 

 ponderance of the forebrain, or cerebral hemispheres, over the 

 mid- and hind-brain. Man's brain is many times larger than 

 that of any other known mammal of equal bulk of body, and 

 three times as large as that of the largest-brained ape. In 



