118 



COMPARATIVE OSTEOLOGY. 



The pectoral arch consists of three parts the scapula, clavicle, and coracoid 

 bone. The scapula is 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 theglenoid cavity for the humerus. The 

 clavicles project downwards and slightly forwards, arching inwards, and 

 generally becoming united below to form a flattened plate, the hypocleideum ; 

 the united clavicles are termed the furculum, 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 ulna is larger 

 and stronger than the radius ; the 

 carpus consists of two bones, the 

 metacarpus of three, one of which 

 as 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 true 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, terminating below in the 

 hypocleideum ; gl, Gleuoid cavity. 



FlG. 40. 



pelvis of a Bird. A, Superior ; B, Lateral aspect ; sm, Sacrum ; II, Ilium ; Is, Ischium ; Am, 

 Acetabuluin. 



