162 BRITISH FOSSIL REPTILES. 



character indicates that its life period far exceeded that of the toothed whale of 

 similar bulk. 



For how many centuries — generation after generation — the great Pliosaurs 

 carried on their predatory wars some feeble conception is afforded by geological 

 inferences from the gradual formation and accumulation of the ocean-beds which 

 have received the dead bodies, and have now revealed to us the insoluble a:id 

 petrifiable parts of the carcases of those cold-blooded carnivores. 



Sterno-coraco-scapular frame {Sauropterygia, Plate 20). — This characteristic 

 part of the skeleton in Sauropterygia being incompletely preserved in that of 

 Plesiosmirus dolichodeirus {8auro])teryg{a, Plate 1), its description has been 

 deferred to the present section, when the perfect condition of the part, subse- 

 quently worked out in another example of the same species (ib., fig. 1), serves 

 to exemplify the modifications of the same jDart in the genus PUosmirus. 



In both o-enera of their order the place and function of a sternum are mainly 

 fulfilled by the pair of coracoids (52, 52) which meet by a longitudinally extended 

 suture (s, s) below the thoracic part of the abdominal cavity. Behind this mesial 

 suture the coracoids diverge and terminate freely by a broad margin, each with 

 an angle inclining laterad (52', 52') . Anteriorly the sutural portions slightly diverge, 

 and expose the end (59') of the mesial plate representing an " episternum ;" laterally 

 each coracoid contracts in length, becomes thickened, and presents two roughened 

 articular siirfaces ; the hinder one (}') contributes the corresponding portion of the 

 articular cavity for the humerus, the fore one (ch) joins the scapula (51) by the suture 

 laterad of which the scapula contributes the free portion {h) of the glenoid cavity. 



In Plesiosmirus (fig. 1) the hinder end of the scapula, which is the thickest 

 part of the bone, is thus divided pretty equally between its coracoidal (ch) and 

 humeral (/') articular surfaces; both are rough or " syndesmosal," the latter least 

 so. In advance of the surfaces {h, ch) the scapula thins and contracts chiefly by a 

 strong margino-mesial concavity contributing the outer border of the " coraco- 

 scapular vacuity " (c s). The outer, thicker border of the scapula, in Plesioscmrus, 

 (fig. 1) is straight, and the bone extending forward expands to unite with the 

 episternum (59) by the suture («A). 



The episternum (59) presents anteriorly a mesial notch, from each angle of 

 which a thicker border extends outward and backward to its sutural union 

 {s li) with the fore end of the scapula. At this union the episternum contracts 

 and is continued backward to join the coracoids, passing a short way internal to 

 them, and appearing externally as a pointed end of the bone at the fore part of 

 the narrow mesial interspace of the coracoids, which interspace interrupts, 

 anteriorly, their extensive mesial sutural union, s, s. 



Thus the sterno-coraco-scapular frame presents an anterior and a posterior 

 notch and a pair of subcircular vacuities. The above-defined characters of this 



