ANATOMY OF VERTEBRATES. 



175 



110 



and Scincus, the ckyicle expands at its medial lialf, which has a 



large vacuity or perforation occupied Ijy membrane. In the 



Chameleon tlic scapular arch is 



as simple as in tlic Crocodile, 



Ijut the coracoid is shorter and 



broader. 



The humerus in Lacertians is 



iisually larger and straighter, fig. 



50, Driico volans, than in the 



Crocodiles, with a more compact 



wall and Avidcr mcdidlary cavity. 



Tiie radius, ib. and fig. 110, h, 



r34, is aluiost straight, and slender, 



witli an oval proximal articular 



concavity, and a distal surface 



partly convex, partly concave. 



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



tlie 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. Tlie Cliameleon offers an exception 

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



direction of the digits modified for the scansorial function in these 

 arboreal Lacertians : I, 11, and iii, enveloped by the skin as tiir 

 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 snjiport and service of the win^s. 

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

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

 Reptiles. The coracoid, strong and straiglit, and coinl)ining, as 

 nsual, witli the scapula to form the glenoid cavity, articulated at 

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

 sternum, which part is produced and keeled. The humerus, ilj. 



BntHls nf rlJl■c■-,^nn Miia fuot, Cliniilrler)!]. CLI. 



