CLASS MAMMALIA. ?3 



have their limbs so much shortened that they can 

 move with facility in the water only, but these cir- 

 cumstances by no means deprive them of the essen- 

 tial characters of the class to which they belong. 



In the whole of this Class the upper jaw is fixed 

 to the cranium ; the lower is composed of two pieces 

 articulated to a condyle, which juts out into a fixed 

 temporal bone. The neck is composed of seven, 

 and in one species of nine, vertebrae. The anterior 

 ribs are attached to a sternum formed of several 

 pieces placed vertically. Their anterior extremity 

 commences from a shoulder-blade not articulated to 

 any other bone, but simply suspended in the flesh, 

 often indeed resting on the sternum by an inter- 

 mediate bone denominated the clavicle. This ex- 

 tremity is continued by an arm, a forearm, and a 

 hand, itself formed of two ranges of little bones 

 called the carpus, another range of bones called the 

 metacarpus, and the fingers each composed of two 

 or three bones called phalanges. 



The posterior extremity of all this class, if we 

 except the cetacea, is fixed to the spine where it 

 forms a girdle, or pelvis, which, in youth, is divided 

 into three pairs of bones, the ilium which is attached 

 to the spine , the pubis which forms the anterior 

 girdle ; and the ischion which forms the posterior. 

 At the point of union of these bones is situated the 

 cavity wherein the thigh is articulated, to which 

 again is attached the leg composed of two bones, 

 the tibia or shin bone and the fibula. The leg is 

 terminated by the foot, the component parts of 



