442 



THE MAMMALS 



Photo by Winchester 



Fig. 28.18. Rhinoceros. The huge "horns" are not true horns but are formed by a 



fusion of hairs. This specimen has a tick bird perched on its back. (From habitat 



group in Chicago Natural History Museum.) 



the hoof. They are often spoken of as the animals with a cloven hoof 

 because of the slit between the two toes. There is one group of the 

 even-toed ungulates which have a special four-chambered stomach. 

 Animals in this group are known as ruminants. They can swallow 

 their food rapidly when they may be grazing out in an exposed place and 

 store this food in a chamber known as the rumen. Then they can retire 

 to a protected place where they can chew the food in leisure. The 

 second chamber, the reticulum, forms a mass of this unchewed food, 

 and it is then regurgitated a mouthful at a time and chewed thoroughly 

 before being swallowed a second time. This time it goes into the third 

 chamber, the psalterium, which is filled with folds that strain out the 

 larger particles and return them to be chewed some more. The well- 

 chewed food passes on into the last chamber, the abomasum, which is the 

 true stomach where the digestive glands are located. Such animals are 

 said to chew a cud. There is an old superstition which holds that a cow 

 must chew a cud in order to be contented and that she will die if she 

 loses her cud. Many a cow has been given a ball of rags to chew on 

 when an owner thought that she had lost her cud. In the ruminants 



