182 BIOLOGY 



holding the arm in position. It is shown from below and 

 flattened out in Figure F. Each half consists of a scapula, sc 

 (the dorsal part of which is made of cartilage), a coracoid, 

 co, a precoracoid and a clavicle fused together, pr. At the 

 place where the coracoid and the scapula come together is a 

 smooth cavity into which the end of the arm articulates, called 

 the glenoid cavity, gc. In its natural position the scapula 

 is bent over the back, with the coracoids touching each other 

 in the middle line below on the ventral side of the body. Be- 

 hind and in front of them are two pieces of bone, the omo- 

 sternum, ost, and the sternum, st. These two bones are re- 

 garded as a part of the axial skeleton. 



The arm proper consists of the humerus (Fig. A, hu), 

 the radius and ulna fused together, r-u, six wrist or carpal 

 bones, c, and five fingers, of which the first is rudimentary. 

 Each finger is composed of a metacarpal, me, and several 

 phalanges, ph. The posterior appendages have a pelvic girdle, 

 made of three pairs of bones, all united into one in the adult. 

 One of them, the ilium, is long and runs forward to the trans- 

 verse process of the last vertebra; Fig. A, il. At its posterior 

 end each ilium joins the other two bones, the pubis (Fig. G, 

 pu), and the ischium, is. At the point where the three bones 

 meet there is a rounded cavity for the attachment of the leg, 

 the acetabulum, ac. The pubes and ischia of the two sides 

 of the body are fused together on the middle line, below the 

 urostyle. The leg consists of a femur (Fig. A, fe), and the 

 crus, cr, which is really composed of a tibia and fibula fused 

 together. Following the crus are the bones of the foot, consist- 

 ing of two slender bones, the astragalus, as, and calcaneum, ca; 

 then come two extremely small tarsal bones, t, and finally 

 a series of metatarsals, mt, and phalanges, ph. 



Muscular System. Most of the bones of the skeleton are 

 more or less movable one upon the other at the articulations. 

 The muscles which move them are numerous and complicated. 

 Each muscle is an elongated mass of contractile tissue, which 



