AMPHIBIA. 185 



sternum) is attached, while posteriorly it broadens out and abuts 

 upon a pair of narrow cartilaginous epi-coracoids. These are 

 succeeded by the sternum proper, a flattened rod of bone, with a 

 core of cartilage. To its hinder end a large, thin, deeply-notched 

 piece of cartilage, the xiphi-sternum, is attached. 



(2) Appendicular Skeleton. The endoskeleton of either the 

 fore- or hind-limb is divisible into (1) Limb-girdle, which is 

 firmly attached to the trunk, and (2) Free limb, articulated to 

 the girdle. 



(a) Fore-Limb. The two shoulder-girdles form an incomplete 

 ring almost encircling the body just behind the atlas vertebra. 

 They are firmly fused to the epi-coracoids, ventrally, while dorsally 

 they are attached by muscles to the skull and vertebral column. 

 Each girdle is made up of a dorsal and a ventral moiety. At 

 their point of union is a shallow, articular, glenoid cavity, affording 

 attachment to the free limb. The dorsal part is made up of 

 (a) The supra-scapula, a quadrangular plate of cartilage, more or 

 less calcified and ossified, broad above, and narrowing downwards 

 to join (b) the scapula, an hour-glass-shaped bone, the lower end 

 of which partly forms the glenoid cavity. The ventral part is 

 composed of (a) The coracoid bone, similar in shape to the scapula, 

 and completing the glenoid cavity. In front of the coracoid there 

 is an oval space filled with connective-tissue, the coracoid fontanelle. 

 This is bounded in front by (b) the prce-coracoid (pr-co), a trans- 

 verse bar of cartilage largely ensheathed by (c) the clavicle, which 

 is the only membrane bone in the appendicular skeleton. 



The free limb is made up of bones supporting the upper arm, 

 fore-arm, and hand. The humerus is a long bone belonging to 

 the first of these. Like the long bones of the limbs generally, it 

 consists of a hollow marrow-containing shaft, and an enlarged 

 epiphi/sis at each end, covered b}' a thin layer of cartilage. The 

 epiphyses remain for a long time distinct from the shaft, with 

 which, however, they ultimately fuse. The proximal end of the 

 humerus forms a rounded head, articulating with the glenoid 

 cavity. A well-marked deltoid ridge, more prominent in the male, 

 runs from this half way along the anterior (ventral) surface of 

 the bone. The distal end presents a spheroidal surface with 

 which the next bone articulates, and above and below this (pre- 

 and post-axially) are condylar ridges. The ante-brachium is sup- 

 ported by a short, stout radio-ulna. This is a compound bone, 



