TO MAMMALS.. Vll 



The thorax is inclosed by ribs, some of which, called the true 

 ribs, are attached to the sternum by a cartilage, the representative 

 of the sternal ribs of other Vertebrata. The posterior ribs are called 

 the false or floating ribs. The sternum is composed of several 

 pieces, and gives attachment to the clavicles when present. The 

 ribs are capable of considerable motion of elevation and depression, 

 aiding the diaphragm in respiration. 



The anterior extremity is fixed to a broad scapula, generally 

 only connected by muscles to the trunk. A clavicle is present in 

 those mammals that use the arm as an instrument of prehension or 

 flight, and the coracoid bone, so conspicuous in other vertebrata, 

 is reduced to an appendage. The rest of the limb is composed of 

 the huraerous,. two bones of the forearm, the radius and ulna, the 

 carpus, metacarpus and phalanges. These last vary much in num- 

 ber. 



The posterior extremity consists of the pelvis, comprising the 

 iliac, ischial and pubic bones, the femur or thigh bone articulated 

 to the iliac bones, the tibia and fibula, tarsus, metatarsus, and 

 phalanges. Modifications of some of these bones and reductions of 

 many of them occur among various Mammals, and will be pointed 

 out in the proper place. 



Considered generally, the muscular system of Mammals varies 

 little from that of Man. The cutaneous muscle is much developed 

 in some, especially in the Porcupine and Hedgehog, by means of 

 which the spines can be suddenly raised. The same is noticeable 

 to a less degree in Dogs and Cats, when they, as it is popularly 

 called, " get their backs up." 



Among Mammals the demand for food is less constant, and the 

 digestive process less rapidly accomplished than in Birds. There 

 is a considerable amount of uniformity in the structure of their 

 digestive organs. The tongue varies much, and is free in most, 

 being only fixed in the Whales. In some it is capable of great 

 extension as in the Ant-eaters and is used to procure food, as it is 

 also, to a certain extent, by some Ruminants. The surface of 

 the tongue is usually covered with papillse, which in some of 

 the Carnivora, the Cat tribe notably, are developed into sharp. 



