INTRODUCTION 3 



arrangement of their bones and joints; but in every particular 

 it will be noticed that the upper limb is constructed with a view 

 to wide scope of movement and lightness, whereas the con- 

 struction of the lower limb tends to stability and weight. They 

 are each attached by a ball-and-socket joint to a bony girdle. 

 But compare the shoulder girdle with the pelvic : the socket in 

 the one case is shallow and much smaller than the ball; in 

 the other the ball is received into a deep socket that covers it 

 up to the neck. The shoulder-girdle is connected anteriorly 

 to the trunk by a loose gliding joint, and posteriorly slung 

 by muscles. The pelvic girdle is firmly welded together in 

 front, and behind is almost immovably joined to the lower 

 vertebrae, whose joints are completely ossified. The reason 

 for this is easily seen when the functions of the upper and 

 lower limbs are compared. 



The Muscular System. The flesh of the body consists of 

 :a number of muscles which are attached at each end to bones. 

 They are capable of contraction, the attachment from which 

 they pull being termed the " origin," and the one on which they 

 pull, the " insertion." A muscle or its tendon passes over one or 

 more joints, and its principal action is on the joint nearest the 

 insertion. 



The Circulatory System. The tissues are nourished by the 

 blood, which is carried to all parts by the arteries and returned 

 T)y the veins. The heart is the starting-point of the system, 

 and by its action the blood is sent on its way at a certain 

 pressure. 



The Respiratory System consists of an air passage from 

 the mouth and nose to the lungs, the latter situated in the 

 thorax, where the blood is reoxygenated. 



The Digestive System consists of the alimentary canal, 

 iDy which food is taken in at the mouth, passed down to the 

 stomach and duodenum to be digested, into the small intestine 

 to be absorbed, and the residue into the large intestine to be 

 excreted. Accessories to the digestive system are the organs 

 which secrete digestive juices and pour them into the alimentary 

 canal. 



The Nervous System is in two parts the cerebro-spinal 



