118 



COMPARATIVE OSTEOLOGY. 



The pectoral arch consists of three parts — the scapula, clavicle, and coracoi(? 

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

 coracoid bone, the strongest of tlie 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 plate, the hypocleideum ; ; 

 the united clavicles are termed the /urcaZwm, familiarly known as the " meiTv^j 



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 

 metabarpus' of three, one of which 

 30 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 anchylo&ed with 



Fio. 39. 

 r Pectoral arch of a Bird, sc. Scapula : co, cora. 

 coid bone ; /, Clavicles, terminating below in the 

 hypocleidemn ; gl, Glenoid cavity. 



fio. 40. 

 pelvis of a Bird A, Superior : B, Lateral aspect : «m. Sacrum ; U, Warn: Is, Ischir ^'^ 

 /▲cetabnlam. 



