384 ELEMENTARY ZOOLOGY 



being usually simple, but sometimes, as in the ruminants 

 and whales, divided into several distinct chambers. The 

 intestine in vegetarian mammals is very long, being in a 

 cow twenty times the length of the body. In the carni- 

 vores 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 composed 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 carbonic-acid gas in 

 turn. At the upper end of the trachea is the larynx or 

 voice-box, consisting of several cartilages attaching by 

 one end to the vocal cords and by the other to 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 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 mr.mmnls, 

 though usually functional in the female only. 



The nervous system and the organs of special sense 

 reach their highest development in the mamnidls. In 

 them the brain is distinguished by its large size, and by 

 the special preponderance of the forebrain or cerebral 



