MIJE-^NOSAUEUS. 115 



lateral facets for contact with one another. The phalanges are ^ery numerous : they 

 are cylindrical and much constricted in the middle; they become smaller and smaller 

 towards the finger-tips, where they may be represented by mere nodules of bone. In 

 the most nearly perfect fore paddle preserved (R. 2864, text-fig. 63, B) the numbers of 

 phalanges in the digits I.-V. are 6, 12, 14, 13, 8. In no specimen has the presence 

 of more than the normal five digits been observed. 



Pelvis (PI. IV. figs. 8, 9 ; PI. V. figs. 8, 9 ; text-fig. 65). — The pelvis is composed 

 of the usual three pairs of bones, and like that of the other Plesiosaurs is chiefly 

 remarkable from the fact, that the three elements of each side do not meet in the 

 acetabulum in a triradiate suture, the ilium having been rotated backwards and its 

 lower end having lost its connection with the pubis. In the early Sauropterygia 

 (text-fig. 64) the pelvis is in this respect of normal type and the peculiarity of this part 

 of the skeleton in the later forms, as in the case of the shoulder-girdle, seems to be 

 the result of the different mechanical conditions brought about by the adoption of an 

 entirely aquatic life. The ilium (PI. IV. figs. 8, 8«; PI. V. figs. 8, 8 «, 8 ^ ; il., text- 

 fig. 65) is a curved rod of bone expanded towards its extremities. The upper end 

 is compressed from within outwards and slightly everted ; the upper end (cr.i.) is 

 obliquely truncated by a surface which was tipped with cartilage in life. The inner, 

 slightly convex face of this expanded upper end is sometimes roughened, as if for 

 \inion with the distal end of the sacral ribs {s.f., PL IV. fig. 8 « ; PI. V. fig. 8), but in 

 other cases is nearly smooth and shows no trace of such union : probably the age of 

 the animal may have something to do with these differences. The shaft also is a little 

 compressed from within out and is oval in section ; it is somewhat curved, the con- 

 cavity being anterior. On the convex posterior border there is a strong ridge forming 

 a projecting angle at about the middle of the bone. The thickened lower end bears 

 two facets — one large and slightly concave, looking forwards, downwards, and outwards 

 for union with the ischium (is.f.) ; the other {acet.) small and continuous with the last, 

 but making an angle with it and looking mainly forwards ; this facet forms the posterior 

 lip of the acetabular surface, and it is continued a little upwards on to the prominent 

 antero-external angle of the distal expansion (PI. V. figs. 8 a, 8 ^, c). Both surfaces 

 were covered with cartilage in life. 



The fuhis (text-fig. 65, p.) is a large plate of bone, the form of which will be best 

 understood from the figure. It is a little wider than long, and the greater part of it is 

 very thin, but towards the outer and anterior borders and in the region of the symphysis 

 it is thickened. The inner border by which the bone unites with its fellow of the 

 opposite side in a median symphysis is straight or convex. The symphysial surface is 

 deepest at about the middle of its length, where the bone is considerably thickened. 

 The anterior border is at first straight or slightly undulated, then it curves outwards 

 and backwards to the somewhat prominent antero-external angle where it joins the outer 

 border; throughout its length this anterior edge is grooved and must have home a 



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