In the Chiroptera the scapula is large and oval, and has a moderately high spine and a large acromion. The coracoid process is well developed and is often forked. The clavicles are also well developed, and vestiges of the precoracoid and of the sternal end of the coracoid are often found.
In Primates the clavicle and coracoid process are always well developed. In Man and the Gorilla the scapula has a long straight suprascapular border, a well-developed coracoid process and spine, and a large curved acromion. Vestiges of the precoracoid occur at each end of the clavicle. The shape of the scapula varies much in the lower Primates.
The Upper arm and Fore-arm.
In the Monotremata the humerus is short, very broad at each end and contracted in the middle. The radius and ulna are stout and of nearly equal size, while the ulna has a greatly expanded olecranon.
In the Marsupialia the humerus is generally a strong bone, broad at the distal end and having well marked deltoid and supinator ridges, which are specially large in Notoryctes. An ent-epicondylar or supracondylar foramen (fig. 105, 5) is almost always present except in Notoryctes. The radius and ulna are always distinct and well developed, and a certain amount of rotation can take place between them. The ulna of Notoryctes has an enormous hooked olecranon which causes the bone to be nearly twice as long as the radius.
Fig. 105. Anterior surface of the right humerus of a Wombat
(Phascolomys latifrons). (After Owen.)
| 1. head. | 6. supinator ridge. |
| 2. greater tuberosity. | 7. external condyle. |
| 3. lesser tuberosity. | 8. internal condyle. |
| 4. deltoid ridge. | 9. articular surface for radius. |
| 5. ent-epicondylar | 10. articular surface for ulna. |
| (supracondylar) foramen. |
Edentata. The Sloths have long slender arm bones; the humerus is nearly smooth and has a very large ent-epicondylar foramen in Choloepus, but not in Bradypus. The radius and ulna can be rotated on one another to a considerable extent. The humerus in all other Edentates is very strong and has the points for the attachment of muscles much developed, especially in the Armadillos and Megatheriidae. An ent-epicondylar foramen is found in all living forms. The radius and ulna are well developed, but are not capable of much rotation.