Prof. Owen on Dicynodon tigriceps. 243 



breadth ; it has articulated with and become anchylosed to a thick and strong 

 parapophysis from the side of the centrum, extending to within a short distance of 

 its hinder end ; it next becomes confluent with a broad and thick neural platform, 

 which expands laterally into the broad depressed diapophysis (d), to the ends of 

 which are traces, in the form of raised borders, of the articulation and actual anchy- 

 losis of the tubercular part of the sacral rib. This rib then augments in breadth, 

 diminishes in depth, and forms a depressed but strong and broad plate of bone, 

 which is bent backwards at a right angle for the extent of seven inches, increasing 

 again in vertical thickness after the bend, where it receives the abutment of the 

 second sacral rib on the inner side, and on the outer side presents a rough concave 

 surface for the iliac bone. The breadth of the neural platform where it forms the 

 hinder zygapophyses is four inches ; the articular surface of those processes looks 

 downwards ; the spine of the first sacral vertebra is broken ; that of the second is 

 short, thick, expanded and truncate at the summit (fig. 4, s). 



The sacral rib of the second vertebra has a similar attachment, by its head, to the 

 upper half of the side of the centrum, and, by the part answering to the tubercle 

 which coalesces with the broad superincumbent neural platform, and extends out- 

 wards, expanding, chiefly in the backward direction, so as to abut upon and overlap 

 the rib cf the foregoing vertebra, and form the upper expanded part of the sacro- 

 iliac surface. 



The length of the middle part of this sacrum or portion of sacrum is between 

 5 and 6 inches ; the breadth is 13 inches. The body of the second sacral vertebra 

 is subcompressed at its middle part, smooth and broadly rounded below. It ter- 

 minates behind in a flat, rough, evidently fractured surface, indicative of its having 

 been violently separated from a third anchylosed sacral vertebra. 



The second sacrum or portion of sacrum (figs. 6 & 7) includes also two anchy- 

 losed vertebrae, the bodies of which present almost the same size and form as those 

 of the preceding specimen : their coadapted ends are completely confluent : the 

 opposite ends are broken ; but on one of these is part of a smooth surface, which 

 indicates it to have formed one end, probably the hinder end, of the sacrum. In 

 each vertebra the sacral rib springs from the confluence of the centrum and neural 

 arch, gradually contracts as it extends outwards, where it presents a full elliptical 

 transverse section ; then again expands, meeting the similarly modified succeeding 

 rib, with which it coalesces to form a sub-bilobed, flat, rough surface (pi) for abut- 

 ment against part of a pelvic arch. In each of these sacral vertebrse the neural 

 spine (fig. 7) expands as it ascends, and terminates in the same broad truncate 

 surface as that of the spine of the preceding sacral specimen (fig. 4, s). It is quite 

 certain that neither of the rib-elements of the second (portion of ?) sacrum can 

 have been modified like the singularly expanded ribs of the first : they have been 



