LIASSIC PLESIOSAURS. 39 



joining the corresponding parts of the pubis ; the outer acetabular angle is produced, 

 and terminally expanded and thickened to form the articular surfaces for the ilium 

 and femur. 



The pubis (ib., 64), as in other Plesiosauri, is broader and larger than the ischium, 

 with the medial or symphysial margin straight, measuring six and a half inches in 

 extent ; the anterior and external free margin is convex ; the posterior margin is more 

 deeply excavated than the opposite one of the ischium, forming a greater part of the 

 circumference of the obturator foramen ; the angle between the posterior and outer 

 borders is thickened, to contribute the anterior part of the acetabulum. This rough 

 and ill-defined articular surface for the femur is thus formed, as usual, by the three 

 constituents of the pelvis. 



The femora (ib., 65) here, as in some other Plesiosauri, have the head resting against 

 the ischio-pubic part of the acetabulum, the ilia being placed about an inch further 

 back. The femur, 10 inches in length, is 1 inch 9 lines across the narrowest part of 

 the shaft, and expands to a breadth of 4 inches 9 lines distally ; the outer (here the 

 upper) part of the head is produced, and behind it is a longitudinal depression. The 

 surface, for two inches or more from the distal end, is rugose, with longitudinal ridges 

 breaking up into tubercles ; both anterior and posterior borders are concave ; the latter 

 is the shorter border. Tlie distal border is more regularly convex, and in a greater 

 degree than in the humerus. 



There is an interval between the proximal ends of the tibia and fibula, and a wider 

 one between their distal ends, the interosseous space being considerable, as in the 

 forearm. Here, also, the tibia (ib., 6G), like its homotype (ib., 54), has a more distal 

 extension. Its length is 3 inches 1 1 lines, its proximal breadth '2 inches 8 lines. The 

 anterior proximal angle is somewhat produced ; the anterior orbital border is slightly 

 concave ; the posterior one is more so. The fibula (ib., 67), like the ulna, departs from 

 the oi'dinary reniform figure by the production of its fibular proximal angle (67') ; this 

 is not separated from the rest of the bone in the left leg, but it is so by what appears 

 to be a crack in the right leg, and yet so as to indicate that such crack is in the place 

 of an original epiphysial junction. The length of the fibula, including this process, is 

 4 inches 4 lines ; the length of the concave tibial border of the fibula in a straight line 

 is 2 inches 3 lines. As great a proportion of the exposed surface of the leg bones is 

 rugose as is that in the bones of the forearm. Between the tibia and the tarsal bone 

 supporting the first metatarsal there is a vacant space in both limbs, which, in the 

 right limb, is partially occupied by a tubercle of bone. This we may regard as the 

 beginning of ossification of a fibro-cartilaginous homologue of a naviculare (Tab. XIV, 

 fig. 3, «). The homotype of the lunare (a) completes, by a free concave part of its 

 border, the distal end of the inter-osseous space. This tarsal («), which we 

 may call " astragalus," articulates with the tibia (66) ; but to a greater extent and 

 by a more definite straight border, with the fibula (ib., &7) ; posteriorly with the 



