PROM THE LOWER LIAS OF CHARMOUTH. 



461 



Restoration of the Pectoral Girdle. (Plate XXIII. fig. 3.) 



The displaced bones retain their original outline so perfectly, that 

 if it were possible to move them relatively to each other into their 

 original positions the pectoral girdle would be well restored ; as, 

 however, the stony matrix in which they are imbedded renders this 

 impossible, I have made careful outline drawings of the several 

 bones, and then cut these out and fitted them together, being guided 

 in doing so by a direct study of the bones themselves. The result 

 is given in the diagram (Plate XXIII. fig. 3). 



The furculum lies in front in the middle line ; and the prescapular 

 processes of the scapulas abut each on its own side upon the outer 

 posterior border of the furcular body proper, covering its wings, 

 which appear to lie in the angle between the ascending scapula and 

 its prescapular process. The lapels face the anterior projecting 

 convexities of the coiacoids without touching them. There is thus 

 produced a single continuous foramen, bounded laterally by the 

 concave inner borders of the scapulas, anteriorly by the furcular 

 lapels, and posteriorly by the anterior margin of the coracoids ; it is 

 wide from side to side, narrow from before backwards, and roughly 

 resembles in form two brackets joined face to face, thus : — C^!D 



In the fact that the foramen is not subdivided into two by the 

 overlapping of the furcular lapels b) T the coracoids, this species differs 

 from some other species of Plesiosaurs ; a corresponding difference 

 is displayed in the pelvic arch, the foramen between the pubes and 

 ischia, likewise double-bracket-shaped, being continuous from side 

 to side, and not divided into two, as happens in most other Plesio- 

 saurs. 



The Humerus. 



The right humerus is carried over to the left side, and lies with 

 its flat posterior surface uppermost (PI. XXIII. fig. 1). Eor the proxi- 

 mal third of its length it is a thick cylindrical bone, with an ellip- 

 tical transverse section, the major axis being twice the length of the 

 minor axis (4 inches and 2 inches respectively) ; it then widens out 

 into a broad plate-like distal portion for the remaining two thirds of 

 its length. The ulnar margin is almost straight, only slightly convex ; 

 the radial more curved and concave. It is covered superficially 

 with irregular longitudinal ridges, more abundant on the radial than 

 the ulnar side, which is almost smooth, and most marked near the 

 ends of the bone ; at the anterior end they become broken up into 

 irregular tubercles. 



The left humerus is similar to the right ; but its surface is 

 smoother, and its proximal half less elliptical or more circular in 

 section ; it begins to widen a little past the middle of its length, 

 widens and flattens then rapidly, becoming very thin (5 inch) 

 towards its distal edge. The more rapid expansion of the left than 

 of the right humerus is almost certainly due to compression, though 

 without the latter bone for comparison we should have nothing to 



