6o 



THE FROG 



ends capped with articular cartilage. The enlarged ends or 

 epiphyses ossify independently of the shaft or diaphysis, 

 with which they do not unite until late in life. The femur 

 (thigh bone) is a good example of a long bone. Examine a 

 dry femur split lengthwise and observe that it is hollow. 

 What are the mechanical advantages of the cylindrical form 

 of the long bones? 



Each anterior limb consists of three parts, upper-arm, 

 fore-arm, and hand. The proximal part of the hand is dis- 

 tinguished as the wrist. 



The upper-arm or brachium contains a single long bone 

 called the humerus. The proximal end or head of the hu- 

 merus rests in the glenoid cavity, forming a ball-and-socket 

 joint, and is held in position by muscles and ligaments. The 

 strong ridge on the preaxial side of the proximal portion of 

 the diaphysis is called the deltoid crest or ridge, and serves 

 for the attachment of muscles. At the distal end is a 

 spheroidal surface for articulation with the bones of the 

 fore-arm. Draw a side view of the humerus ( X 2). 



The fore-arm contains likewise but a single bone, the 

 radio-ulna. This is formed by the fusion of two originally 

 distinct bones (compare the human skeleton). The distal 

 half is imperfectly divided by a groove into preaxial or 

 radial, and postaxial or ulnar, portions. The proximal end 

 is hollowed out to articulate with the distal end of the 

 humerus, and bears a projection known as the olecranon 

 process. 



The wrist or carpus contains six small carpal bones ar- 

 ranged in two rows. In the proximal row there are three 

 bones: one corresponding to the radius, the radiale; one 

 corresponding to the ulna, the ulnare; and one between 



