AN ANOilODONT REPTILE. 



269 



bular border of the ischium : the " tuberosity " is indicated at t, fig-. 2. 

 The extensive ischio-pubic symphysis (fig. 2, y, y) may have been 

 obliterated by continuous ossification, as in the pelvis of Dicynoclon 

 above compared*, where it projects, ridge-like, between the broad, 

 outwardly concave, ischio-pubic plates. The parts of the dorsal 

 surface of the plates of Platypodosaums exposed in the block of 

 matrix show the hinder half of a continuous crest of bone (ib.fig.3,ns), 

 due to confluence of the neural spines of the third, fourth, and fifth 

 sacrals. It may have been continued further forward. 



The last lumbar vertebra (ib. fig. 5) shows the hinder concave 

 articular surface of the centrum, c, which is 2 inches 3 lines in dia- 

 meter. The margin of the concavity is thick and convex, as in the 

 dorsal vertebra {Joe. cit. p. 414, pi. xvi. fig. 3) of the preceding paper 

 on Platypcdosaurus. The neural canal, m, is 7 lines in diameter at 

 its hinder outlet, m. The neurapophyses, n, n, rise to 10 lines before 

 sending off the diapophyses, which are broad and flat above, and 

 give attachment to a slightly curved pleurapophysis, pi, 4| inches 

 in length and 9 lines in breadth ; at its free end it almost comes 

 into contact with the iliac labrum. 



Of all the examples of pelvic structures in extinct Eeptilia which 

 have come under my observation, the type of pelvis exemplified in 

 Platypodosaurns departs furthest from any of the modifications of 

 that part of the skeleton known in existing Eeptilia, and at the same 

 time makes the nearest approach to the Mammalian pelvis. This is 

 seen, not only in the number of sacral vertebrae, but in their breadth, 

 due to the outward extension of their expanded transverse processes. 

 The Mammalian character is more marked by the breadth of the iliac 

 bones, and by the extent of confluence of the similarly expanded 

 ischia and pubes, together with their further confluence at the 

 ischio-pubic symphysis (which, though the bones are here fractured 

 in the present example, may be inferred to have existed from the 

 general resemblance of the pelvis of Dicynoclon to that of Platypodo- 

 saurus). 



The small solution of continuity between the ischium and ilium 

 shown by the foramen (o, fig. 2, PI. X.) closely accords with the 

 foramen in a similar part of the pubis of many modern lizards, which 

 gives passage to the " superficial femoral artery." It may, however, 

 if the ischium be actually continued into its periphery in Platypo- 

 dosaurus, be regarded as a trace of a " foramen obturatorium." 



EXPLANATION OF PLATE X. 



Platypodosaurns robustus. 



Pig. 1. Front view of pelvis: ^ nat. size. 



2. Side view of acetabulum, ischium, and pubis : ^ nat. size. 



3. Back view of sacrum and iliac bones : \ nat. size. 



4. Section of ilium anterior to the acetabulum : nat. size. 



5. Back yiew of last lumbar vertebra : nat. size. 



Loc. cit. 



