ANATOMY OF VERTEBRATES. 



175 



110 



and Scincus, the clavicle expands at Its medial half, which has a 



large vacuity or perforation occupied by membrane. In the 



Chameleon the scapular arch is 



as simple as in the Crocodile, 



but the coracoid is shorter and 



broader. 



The humerus in Lacertians is 

 usually larger and straighter, fig. 

 50, Draco volans, than in the 

 Crocodiles, with a more compact 

 wall and wider medullary cavity. 

 The radius, ib. and fig. 110, b, 

 54, is almost straight, and slender, 

 with an oval proximal articular 

 concavity, and a distal surface 

 partly convex, partly concave. 

 The ulna, fig. 110, a, 55, shows 

 the olecranon better developed 

 than in the Crocodile : its dis- 

 tal articular surface is convex. 

 The digits are five in number, 

 the phalanges are 2, 3, 4, 5 and 3, 

 counting from the metacarpal of 

 the first to that of the fifth digit : 

 each has a claw supported on 

 a moderately long, compressed, 



curved, and pointed phalanx. The Chameleon offers an exception 

 to the numerical rule, the phalanges being 2, 3, 4, 4, 3 ; and the 

 direction of the digits modified for the scansorial function in these 

 arboreal Lacertians : I, II, and in, enveloped by the skin as far 

 as the claws, are directed forward ; iv, and v, similarly sheathed, 

 are directed backward : and the joints are shorter and broader than 

 in Land-lizards. 



The fore limbs in Draco volans accord with the usual lacertian 

 type, and take no share in the support of the parachute. But 

 in the extinct order of truly volant Reptiles {Pterosauria) they 

 were modified for the exclusive support and service of the wings. 

 The scapula, fig. Ill, 51, long, narrow, flattened, and slightly 

 expanded, lay more parallel with the spine than in land and sea 

 Reptiles. The coracoid, strong and straight, and combining, as 

 usual, with the scapula to form the glenoid cavity, articulated at 

 the opposite end with a groove at the fore-part of a discoid 

 sternum, Avhich part is produced and keeled. The humerus, ib. 



Bonds of fore-arm and foot, Chameleon, cm. 



