10 FOSSIL REPTILIA OF THE 



The transverse process has subsided to a tubercle upon the eighteenth (ib., 

 fig. 1, d), and the postzygapophysis to a notch at the back part of the base of the 

 neural spine, but the prezygapophysis (*) continues long and slender throughout 

 this series. The neural spijies progressively narrow and shorten, with a backward 

 inclination. The base of the haemal spine (h) of the sixteenth caudal measures 

 9 lines ; its articular surface is transversely oblong. The surface for the arti- 

 culation of the haemal arch, from this part of the tail onward, is chiefly afforded 

 by the hinder and under part of its own vertebra, as in fig. 3, h. The haemal arch 

 and spine becomes reduced in the eighteenth caudal to the length of its centrum; 

 and in the twenty-third becomes shorter than the centrum, with a greater degree 

 of antero-posterior expansion of the spine in proportion to the length of that, part 

 (ib., fig. 1, 23, h)- The transverse diameter of the anterior articular surface of the 

 nineteenth caudal is 1 inch 6 lines. The middle of the centrum has been reduced 

 by pressure, attended with some fracture of the outer surface, to a diameter of 7 

 lines. In some of these vertebras the middle, crushed parts of the centrum have 

 been severed from the terminal articular expansions. I conclude, therefore, that 

 they have been subjected to a general compressive force, probably connected with 

 the change in the vertical relative position of the stratum. The compact layer of 

 osseous tissue forming the articular end has resisted the pressure ; the intervening, 

 intermediate, cancellous structure has yielded to it. 



From three smaller portions of the matrix, succeeding the ninth block, eleven 

 consecutive caudal vertebrae were wrought out, as in Tab. IX, fig. 2, making us 

 acquainted with a total of thirty-five caudal vertebrae of Scelidosaurus. In the last 

 of this series the centrum (ib., 35) is reduced to the length of 1 inch, and the breadth 

 of its front articular end to 6 lines. In the twenty-fifth caudal vertebra the centrum 

 (ib., fig. 3) is 1 inch \0\ lines in length, 1 inch 3 lines across the articular end, 7^ 

 lines across the middle, the longitudinal concavity of the sides exceeding that of 

 the under surface. At the fore part of this surface the haemapophysial articulation 

 is barely indicated ; at the back part it is marked by two surfaces (h), towards the 

 most prominent part of which short, low ridges diverge. The low neural arch 

 has coalesced with the upper three fourths of the centrum ; the prezygapophyses 

 (*) overhang the free fore part of the centrum, and extend beyond it to clasp 

 the back part of the preposed neural spine. This is represented by a short, com- 

 pressed ridge projecting above the part clasped by the prezygapophyses. The 

 haemal arch of the twenty-fourth caudal (ib., fig. 2, 24, h) underlies the centrum of 

 the twenty-fifth ; it presents a length of 1 inch 6 lines. Its closed base (ib., fig. 4) 

 has a breadth of *l\ lines ; it presents a sub-bilobed form, concave transversely, 

 convex from before backward. At the sides of the haemal canal or rather slit, the 

 arch has a fore-and-aft breadth of 4 lines, the spine expands to twice that extent, 

 with an obtusely rounded termination. In the twenty-seventh caudal vertebra 



