ANATOMY OF VERTEBRATES. 171 



Tlie scapula, 51, is sliort and straight, displaced ])ackward from 

 the occiput, and contributing to form the shoulder-joint, as in the 

 Batrdclua and higher air-breathers : hut it sliows a certain breadth 

 and flatness. The coracoid, 52, is still broader, not cartilaginous 

 as in most perennibranchs, but well ossified, and united below 

 with its fellow, and with a small ' episternum ' of a triradiate 

 form, one ray of which is wedged into the fore part of the 

 mtercoracoid fissure. There is also a pair of bones, 50, long and 

 slender, articulated with the fore border of the scapula and the 

 transverse rays of the episternum : they are the cla^'icles. A 

 supplementary flattened bone, the ' epicoracoid,' is wedged between 

 the scapula, clavicle, and coracoid. The above complex and 

 powerful scapular arch would enable the fore-paddles to act upon 

 the land with sufficient power to effect a shuffling forAvard move- 

 ment of the body, as in the Turtle {Cliehnu;) and Seal tribe: but 

 the main office of the fore-limb in the Ichthyosaur was that of a 

 pectoral fin. 



In the Plesiosaurus, fig. 45, the limbs acquired a developcment 

 more closely accordant with that in Chdona. The scapula, r>i, 

 developes an acromial process representing the clavicle. The 

 coracoid, 52, is unusually extended in the trunk's axis, and is united 

 with its fellow by a long symiihysis interposed between the an- 

 terior abdominal rib and the episternum ; it articulates at its fore 

 part with the episternum and clavicular process, and, further back, 

 with the lower end of tlie scapida to form the humeral joint. 



The humerus is proportionally longer than in IcMlujosaurus ; 

 the radius is better developed, and slightly expanded at both ends ; 

 the ulna retains a flattened reniform shape. The cardial scries is 

 distinct, in a double row of ossicles, the largest at the radial side 

 of the wrist, the opposite side retaining more imossified material. 

 The tligits are five in number, with the proximal and more elongated 

 joints representing a metacarpus. The jjhalanges are shorter, and 

 decrease in size to the tips of the digits, which converge. The 

 first or radial digit ha^ generally 3 j'halanges, the second from 5 

 to 7, the third 8 or 9, tJie fourth 8, the fifth 5 or 6 : all are flattened 

 and included in a common sheath of integument like those of the 

 Turtle ; but the paddle had no claws. 



The scapular arch retains the same essential simplicity in the 

 Chelonian as in the Sauropterygian order, only the acromial or 

 clavicular process is relatively longer', more like a collar bone ; it 

 extends from irear the articular part of the scapula toward the 

 median line, in advance of the coracoid, fig. 51, o, with tl 



ie 



medial end ligameutously attached to the episternal. In the 



