IO50 CLASS REPTILIA. 



surface of the abdomen, and consist of a median and two lateral 

 moieties. 



In the pectoral girdle the scapula is generally a more or less 

 elongated bone, with an expansion at its glenoidal extremity. A 

 separately ossified precoracoid exists only in the Anomodonts (fig. 

 978 Ms), this bone being in other cases fused either with the 

 scapula, as in the Chelonia (fig. 1008), or with the coracoid, as in 

 Lizards (fig. 830); the fontanelle which frequently occurs in the 

 latter instances apparently marking the original line of separation 

 of the two bones. The coracoid may vary in shape from a long 

 spatulate form (Chelonia) to that of a cheese-cutter (Dinosauria). 



The humerus has in many cases no distinct distal condyles 

 (trochlear), although these are well developed in the Anomodonts, 

 Lizards, and Sphenodon. In the more generalised types there is fre- 

 quently an entepicondylar foramen to this bone, but in the Lizards 

 and Chelonians the foramen or groove is ectepicondylar ; and in a 

 few instances both foramina are present. The radius and ulna 

 always remain distinct. The number of bones in the carpus varies 

 considerably in the different orders, but in Sphenodon alone among 

 existing forms is there more than a single centrale ; the five distal 

 bones (carpalia) may be all distinct from one another (fig. 829). In 

 the pelvis of the majority of reptiles, the ilium is produced more 

 behind than in front of the acetabulum (fig. 831), and the latter is 

 more or less completely closed by bone; while the pubis (fig. 831) 

 is directed downwards and forwards, and, like the ischium, usually 

 meets its fellow in a ventral symphysis. Among the Dinosaurians, 

 however, the pelvis may be of a Bird-like type, when the pubes do 

 not form a symphysis. Usually the obturator interval forms an 

 open notch ; but by the ventral union of the pubis and ischium of 

 the same side this notch may be converted into a foramen. The 

 femur among the Dinosaurs may develop an inner trochanter ; and, 

 except in some Ornithosauria, the fibula always remains distinct 

 from the tibia. As in the carpus, the elements of the tarsus vary 

 considerably in the different groups, but the centrale (navicular) is 

 only present in the Anomodontia, the Proterosauria (according to 

 Professor Seeley), one family of Chelonians, and the Ichthyo- 

 pterygia ; while, with the exception of a few extinct types, and perhaps 

 the existing Chelonia, the fourth and fifth tarsalia in all land forms 

 coalesce into a single bone, which supports the fourth and fifth 

 metatarsals. In certain groups — such as the Anomodontia and 

 many of the Chelonia (fig. 829) — the number of phalangeals in the 

 feet of pentedactylate forms may be the same as in Mammals, or 

 2 ? 3) 3> 3> 3 — tne digits being reckoned from the first to the fifth. 

 In Lizards, however, and their allies the number of phalangeals is 

 usually 2, 3, 4, 5, 3 in the manus, and 2, 3, 4, 5, 4 in the pes. 



