562 BRITISH FOSSIL REPTILES. 



projecting a cbuple of inches in advance of the second sacral rib (ib., pi- 2). The Ion" or 

 vertical diameter of the head or articular end of this rib-plate is 6 inches ; at 3 inches 

 of its outward course it expands to a breadth of 1\ inches by a convex extension of the 

 fore border, which appears to have articulated like a rib-tubercle with the neural arch, and 

 to have been underlapped by part of the ilium (PI. 72, a). Beyond this point the rib- 

 plate, as it approaches the acetabulum, diminishes in breadth but increases in thickness 

 and seems to develop from its haemal side a broad, transversely convex ridge or buttress 

 (ib., pi. 1) 5 inches long by 2^ broad at the distal end, which abuts upon the fore and 

 haemal angle of the acetabulum, e. A process of the antacetabular part of the ilium (ib., a) 

 is continued inward and hseniad to articulate with the upper border of this first broad, 

 sacral rib ; an oblong vacuity, 4 inches by 2 inches, intervenes between this process of 

 the ilium and the acetabulum. The second sacral rib (ib., pi. 2) is indicated by the part 

 of the plate posterior to pi- i- 



The ])roximal portion of this seemingly single broad and bifid pleurapophysis is 

 applied to the greater part of the sides of the two anterior sacral centrums (it)., s \, s 2), 

 showing it to be the confiuence of two pleurapophyses, the part described as the convex 

 side or buttress being the distal articular end of the anterior of these. 



On this view the next independent sacral rib would be the third (ib., pi. 3) ; its proximal 

 end is expanded and applied by a similar, but not so great, obliquity to the side of the 

 third sacral centrunj (ib., « 3), having a breadth of 3 inches with a thickness of nearly 

 2 inches, but contracting to a narrow rounded haemal border, retaining above this part a 

 thickness of 1 inch, then expanding to a breadth of 3 inches to abut upon the htemal 

 border of the acetabular part of the ilium, filhng the interval between the like extremities 

 of the second and fourth sacial ribs. The direction of the third pair is nearly trans- 

 versely outward. The length of the interspace between the second and third ribs is 

 , inches ; the fore-and-aft breadth is 3^ inches ; it narrows towards the acetabulum, 

 where the distal expansions of these ribbed buttresses come into contact and seemingly 

 coalesce with each other, and similarly narrows to their })roxinial expansions, thus showing 

 an elliptical shape. 



The head of the fourth sacral rib (ib., pi. 4) is applied to the whole side of the 

 corresponding centrum (« 4), and is S^ inches in fore-and-aft diameter; from this the 

 rib contracts to the form of a subvertical thick ])late, and then expands to a breadth 

 of 4 inches applied to, and confluent with, the lower border of the acetabulum and a 

 considei'able extent of the medial surface of the ilium rising tiierefrom. 



The fifth sacral rib, with the head reduced to 2^ inches in fore-and-aft extent, is 

 applied to the side of the last sacral centrum (« 5). This rib, contracting at first like the 

 previous ones, then expands as it extends outwards and slightly backwards, chiefly in 

 the vertical direction, to be applied for an extent of 5 inches to the part of the 

 acetabulum to which the ischium is articulated. A considerable part of the right 

 ischium (ib. 63) is retained, dislocated a few inches from the articular facets (ib., b, c), 



