THE LIMBS. 237 



Shoulder girdle and wings. The peculiarities of the anterior ex- 

 tremities are connected with their transformation into wings. Their 

 connection with the thorax is always a firm one, since flying organs, 

 whose movement pre-supposes a great expenditure of muscular power, 

 require the necessary support on the trunk. While the scapula, 

 which is a long, sabre-shaped bone, lies along the dorsal side of the 

 thoracic framework, the clavicle and coracoid, as pillar-like supports 

 for the shoulder-joint, are attached to the sternum. The two clavicles 

 are fused so as to form a fork (furcula). The anterior extremity 

 consists of a humerus, a longer forearm composed of radius and ulna, 

 and the reduced hand. The latter contains only two carpal bones, 

 an elongated metacarpus and three fingers viz., the pollex or thumb, 

 bearing the so-called bastard wing (alula), a middle finger, and a 

 little finger. The humerus, the forearm, and the hand are so 

 placed when at rest, that the humerus is directed backwards, the 

 long forearm lies tolerably parallel to it and is directed forwards, 

 while the hand is again bent backwards. 



Pelvic girdle and legs. The girdle of the hind limbs has the 

 form of an elongated pelvis connected with a great number of lumbar 

 and sacral vertebrae, and except in the ostrich (Struthio camelus) is 

 without a symphysis pubis. The short and powerful femur is directed 

 obliquely horizontally forwards, and concealed beneath the flesh 

 and feathers \pf the abdomen, in such a manner that the knee-joint 

 is not visible externally. The crus, which is much longer and more 

 extensive, is chiefly composed of the tibia, the fibula being quite 

 rudimentary and represented by a styliform bone on the outer side 

 of the tibia. The crus is always followed by a long f orwardly directed 

 bone the tarso-melatarsus which is composed of the fused tarsal 

 bones of the distal row (inter tar sal joint), and of the metatarsal bones. 

 The tarso-metatarsus varies much in length, and is the cause of the 

 differences in the length of leg. At its lower end it divides into 

 three processes, which are provided with articulating heads, for the 

 attachment of the same number of toes. When a fourth toe is 

 present, there is always a small bone on the inner side of the meta- 

 tarsus, and to this bone the fourth inner toe is attached. The three 

 or four toes (only in one case is the number reduced to two) are 

 composed of several phalanges, the number of which increases from 

 within outwards in such a manner that the first toe has two, the 

 fourth (external) five joints. 



[The digits present in the Avian pes are Nos. 1, 2, 3, 4, or 2, 3, 4, 

 or in the Ostrich 3, 4. Digit No. 5 is never present.] 



