44 PROF. OWEN ON SOME DINOSAT7RIAN VERTEBRA. 



A vertical longitudinal section was then made of a dorsal centrum. 

 A fine, close, cancellous texture prevailed, more compact at the peri- 

 phery, with a slight enlargement of the cancelli toward the centre. 

 The central pit or foramen led to a cylindrical canal 6 lines long, 

 slightly expanding, and then rapidly contracting to a point (PI. IV. 

 fig. 1 a, c'), which met the apex of the opposite cone at the middle of 

 the centrum. Each canal had admitted the original mud of the matrix 

 to near the hase of the cone ; but that cavity contained crystals of 

 spar, with matrix of a lighter colour than the rest. Some substance 

 in the recent carcass had resisted further entry of the mud until the 

 whole had hardened, and in the remaining cavities spar had slowly 

 crystallized. 



In developing from a similar almost intractable matrix the parts 

 of the skeleton of another genus (Pareiasaurus, Ow.) of phytopha- 

 gous Dinosaur, the dorso-lumbar vertebrae of a species (Par. bom- 

 bidens) of somewhat smaller size than Tapinocephalus Atherstonii 

 presented centrums proportionally longer to their breadth and height 

 than in the representative of the latter genus. A centrum 3 

 inches 9 lines in breadth, and 3 inches 4 lines in height, has a 

 length of 2 inches 8 lines along its lower part. 



The articular surface of the centrum is subundulate, convex along a 

 fourth of the periphery, concave at the centre, feebly so at both parts, 

 and with the slight convexity continuing from the upper border to 

 near the centre. The appearance of any pit here was so inappreci- 

 able that the tentative section of the first centrum so divided was 

 made with little expectation of a repetition of the canaliculo-coni- 

 cal excavation. There it was, however (PL Y. fig. 3, c, c') ; its 

 aperture or outlet a little wider relatively, the entering canal rather 

 more constricted, the terminal cone with a somewhat dilated base, 

 and an interval of the osseous texture, of two to four lines extent, 

 separating the apices. Here also, the canal was filled by matrix, 

 the cone by mixed discoloured matrix and spar. 



Save as regards this central depression, the articular surfaces of 

 the Pareiasaurian centrums, like those of Tapinocephalus, would be 

 most correctly characterized as "amphiplatyan." But a vertebra of 

 the same column of Pareiasaurus bombidens, of somewhat smaller 

 size (PI. V. figs. 4-7) deepened so regularly beyond the peripheral 

 convexity of the articular surface of the centrum as to entitle it to 

 be characterized as " amphicoelian." From this character, which, 

 in some cases is approached by the caudal vertebrae of amphiplatyan 

 columns, I was at first disposed to view this vertebra as caudal, 

 more especially as the lower border of both terminal surfaces was 

 obliquely bevelled off, the anterior one (figs. 4 & 5, Jiy) in a great 

 degree, and roughened as if for ligamentous or synchondrosal 

 attachment of a haem- or hypapophysis. 



But with the foregoing characters were associated a wide neural 

 canal (ib. fig. 6, n), a parapophysis near the lower part of the side 

 of the centrum (ib. fig. 5,^), and the base of a diapophysis (d) out- 

 standing from the basal part of the neurapophysis (np). These cha- 

 racters determine the vertebra to be cervical, and perhaps the an- 



