66 OSTEOLOGICAL GALLERY. 



Passing to the appendicular skeleton, we have to notice first the 

 anterior or shoulder-girdle, which in Mammals consists generally 

 of only two separate bones the clavicle or collar-bone, very often 

 absent or imperfectly developed ; and the scapula (sc) or shoulder- 

 blade, to which latter there is firmly united a small projection of 

 bone, the coracoid (cr), representing a third girdle-bone, which is 

 separate in Birds, Reptiles, and Fishes, and also in the Mono- 

 tremes, the lowest of all the Mammalia. 



The scapula is a more or less flattened triangular bone placed 

 outside the ribs, but not attached to them by bone, and with its 

 narrow end directed towards the ventral side of the body. At this 

 narrow end there is a hollow socket into which the head of the 

 upper arm-bone fits. Down the centre of the scapula on its outer 

 surface runs a long prominent ridge, which terminates below in a 

 prolonged process (acromiori), to the tip of which the collar-bone, 

 when present, is attached ; its other end being united to the upper 

 part of the breast-bone. 



The humerus (h), or upper arm, is the powerful bone placed 

 between the shoulder and elbow, and articulating above with the 

 scapula by a ball-and-socket joint, and below with the radius (r) 

 and ulna (u), the bones of the forearm, by a simple hinge-joint 

 allowing motion in one direction only. 



The two bones of the forearm are joined below to the wrist- 

 bones, collectively called the carpus (cp), and succeeded first by 

 the metacarpals (fflp), or palm-bones, and then by the phalanges 

 (ph), or finger-bones, usually three to each properly-developed 

 digit. 



The posterior girdle or pelvis (pv) is comparatively strong and 

 rigid, firmly attached to the sacral part of the vertebral column. 

 Originally it consists of three distinct bones on each side the 

 ilium (il), ischium (isch), and pubis (pb), corresponding, the first 

 to the scapula, and the two latter together to the coracoid ; but 

 soon they are so completely united as to appear to be but a single 

 bone. 



The hind limbs themselves consist of a similar set of bones to 

 those of the anterior pair, viz. the femur (fm), or thigh-bone, corre- 

 sponding to the humerus, followed by the tibia (tb) and fibula (fb), 

 or shin-bones, representing the radius and ulna ; the tarsus (is), or 



