THE SKELETON. 77 



course this does not mean that men were developed from 

 tadpoles. 



The Appendicular Skeleton. This consists of the 

 shoulder-girdle and the bones of the fore limbs, and the 

 pelvic girdle and -the bones of the posterior limbs. The two 

 supporting girdles in their natural position with reference to 

 the trunk skeleton are represented in Fig. 32. 



The Shoulder-girdle, or Pectoral Arch. This is made 

 up, on each side, of the scapula or shoulder-blade, and the 

 clavicle or collar-bone. 



The scapula (S, Fig. 32) is a flattish triangular bone 

 which can readily be felt on the back of the thorax. It is 

 not directly articulated to the axial skeleton, but lies im- 

 bedded in the muscles and other parts outside the ribs on each 

 side of the vertebral column. From its dorsal side arises a 

 crest to which the outer end of the collar-bone is fixed, and 

 on its outer edge is a shallow cup into which the top of the 

 arm-bone fits: this hollow is known as the glenoid fossa. 



The collar-bone (C, Fig. 32) is cylindrical and attached at 

 its inner end to the sternum as shown in the figure, fitting 

 into the notch represented at Id in Fig. 27. 



The Fore Limb. In the limb itself (Fig. 33) are thirty 

 bones. The largest, a, lies in the upper arm, and is called the 

 humerus. At the elbow the humerus is succeeded by two 

 bones, the radius and ulna, c and b, which lie side by side, 

 the radius being on the thumb side. At the distal ends of 

 these bones come eight small ones, closely packed and forming 

 the wrist, or carpus. Then corno five cylindrical bones 

 which can be felt through the soft parts in the palm of the 

 hand; one for the thumb, and one for each of the fingers. 

 These are the metacarpal bones, and are distinguished as first, 

 second, third, and so on, the first being that of the thumb. 

 In the thumb itself are two bones, and in each finger three, 

 arranged in rows one after the other; these bones are all called 

 phalanges . 



The Pelvic Girdle (Fig. 32). This consists of a large 

 bone, the os innominatum, Oc, on each side, which is firmly 

 fixed dorsally to the sacrum and meets its fellow in the mid- 

 dle ventral line. In the child each os innominatum consists 

 of three bones, viz., the ilium, the ischium, and pubis. 

 Where these three bones meet and finally ankylose there is a 

 deep socket, the acrtabulum, into which the head of the thigh- 



