118 



COMPARATIVE OSTEOLOGY. 



The 2)Scto7ril arch consists of tliree parts — the scapula, clavicle, and coracoid 

 bone. The scapula i? sword-shaped, and placed nearly horizontally ; the 

 coracoid bone, the strongest of the three, is almost perpendicular, and firmly 

 attached to the sternum below, affording a strong basis for the bones of the 

 wing to move upon ; it helps to form the glenoid cavity for the humerus. The 

 clavicles project downwards and slightly forwards, arching inwards, and 

 generally becoming united below to form a flattened j)late, the hypodeidcum ; 

 the united clavicles are termed i\\Q furcuhLm, familiarly known as the "merry- 

 thought." The hypocleideum is 

 usually joined by a ligament to the 

 sternum below ; in some classes of 

 birds it is absent ; in some the 

 clavicles are not united ; in some 

 again they are united by ossification 

 to the sternum. The ^dna is larger 

 and stronger than the radius; the 

 carpus consists of two bones, the 

 metacarpus of three, one of which 

 is a rudimentary pollex. There are 

 two digits, one of which has one, the 

 other two or three phalanges. 



The pelvis is expanded and shield- 

 like, and consists of the ilium, 

 ischium, and pubis ; but there is 

 no inferior symphysis, and, therefore, no tnte pelvic cavity. The pubis is 

 styliform, and directed backwards and inwards ; in the ostrich alone it articu- 

 lates with its fellow. The femur is short, the tibia long, and anchylosed with 



Fig. 39. 

 Pectoral arch of a Bird, sc, Scapula ; co, cora- 

 coid bone ; /, Clavicles, tenninating below in the 

 hypocleideum ; gl. Glenoid cavity. 



Fig. 40. 

 Pelvis of a Bird. A, Superior; B, Lateral aspect; sm, Sacrum; II, Ilium; /.<, Ischium; Ai 

 Acetabulum. 



