The episternum (fig. 30, A, 10) is a thin almost circular plate of cartilage much of which remains hyaline.
The omosternum (fig. 30, A, 11) is a slender bony rod widest at its posterior end; it connects the episternum with the ventral ends of the precoracoids.
The sternum proper is a short rod of cartilage sheathed in bone; it is contracted in the middle and expanded at each end. It bears attached to its posterior end a broad somewhat bilobed plate of partially calcified cartilage, the xiphisternum (fig. 30, A, 13).
B. The Anterior limb.
This is divisible into three parts, the upper arm or brachium, the fore-arm or antibrachium, and the manus.
All the larger bones have their ends formed by prominent epiphyses which do not unite with the shaft till late in life. Their articulating surfaces are covered by hyaline cartilage.
In the upper arm there is a single bone, the humerus.
This has a more or less cylindrical shaft and articulates by a prominent rounded head with the glenoid cavity. The distal end shows a large rounded swelling on either side of which is a condylar ridge, the inner or postaxial one being the larger. A prominent deltoid ridge runs along the proximal half of the anterior surface, and in the male frog a second equally prominent ridge runs along the distal half of the posterior surface.
The fore-arm consists of two bones, the radius and ulna, united together and forming the radio-ulna. The two bones are quite fused at their proximal ends where they form a deep cup which articulates with the distal end of the humerus, and is drawn out into a rather prominent backwardly-projecting olecranon process, which ossifies from a centre distinct from that of the shaft. The distal end is distinctly divided by a groove into an anterior radial and a posterior ulnar portion.
The manus consists of two parts, the wrist or carpus and the hand.