Osseous System. 161 



FIG. 84. Sternum and Pectoral 

 Arch and right arm of Bird Pen- 

 guin Aptenodytes . 



1 1, Scapula. 



2 2. Coracoid. 



3 3, Clavicles. 



4, Glenoid Cavity. 



5, Humerus (Upper Arm). 



6, 7, Radius and Ulna, 



8, 9. Metacarpals (Hand bones). 



10, Phalanges (or rudimentary fingers). 



11, Sternum. 



12, Keel of Sternum. 



In birds the f urcula, or < c merry thought " 

 or "wish bone," is formed of the two 

 clavicles joined together in front instead of 

 being separately articulated with the sternum. 



The scapula and coracoid together form the L-shaped bone on each 

 side of the neck, the coracoid part being the stout heavy end which is 

 joined to the sternum in front and serves, with the clavicle, to keep the 

 shoulders apart against the powerful compression strain caused by the 

 action of flying. The flat, blade-like end of the L is the Scapula, or 

 shoulder blade. Parrots, however, have a weak f urcula or clavicle, and 

 some paroquets none at all, while those of the Toucans are not connected 

 in front, but subsist as a pair of straight and sharp practically useless 

 rudiments. But in these birds the coracoids are well developed. In 

 the extinct Pterodactyls, the parts are similar to those of the Parrot^ 

 &c. , in having no clavicles, but possessing the coracoid. 



The Monotremes, Echidna and Ornithorhynchus, which possess so 

 many bird and reptilian characters, resemble the birds, amphibians and 

 lizzards in the form of the pectoral arch, the coracoid being large and 

 articulating with the sternum, and also possessing the attachment found 

 in Amphibia known as the epicoracoid. Their clavicles also are peculiar 

 in being articulated in front to a T-shaped inter-clavicle, which is found 

 in no other mammals but which is a reptilian feature, and is represented 

 in the skeleton of the extinct reptile Ichthyosaurus. 



In none of the rest of the mammals does the coracoid articulate with 

 the sternum, but where there is any at all it appears as only a remnant 

 attached as a process to the scapula. The only strut left between the 

 scapula and the sternum is, then, the clavicle, and in many tribes even 

 that is discontinued. In the Marsupials (Kangaroo, &c.), the coracoid 

 is a considerable rudiment but does not come near the sternum. 



Of the Edentates some of the species possess clavicles, for example, 



